“A required .DLL File, AC1st15.dll, was not found”
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallThe ac1st15.dll missing error means a legacy Autodesk-based application cannot load its Autodesk ObjectDBX library. It is not a Windows system DLL, so the safest solution is to identify the Autodesk program that owns it and repair or reinstall that program.
You may also see:
- “This application failed to start because ac1st15.dll was not found. Re-installing the application may fix this problem.”
- “ac1st15.dll is missing.”
- “Failed to load ac1st15.dll.”
- “Cannot find ac1st15.dll.”
- “Page fault in module ac1st15.dll.”
- “The procedure entry point
_acFREE@@YIXPAX@Zcould not be located in the dynamic link library ac1st15.dll.”
Which fix applies to you
Use this list to choose the right starting point:
-
The error appeared after moving, restoring, or reinstalling Windows
Repair or reinstall the original Autodesk application. -
The file disappeared suddenly
Check your antivirus quarantine and security history before changing anything. -
The file exists, but Windows reports a missing procedure or the application crashes
Suspect an incompatible DLL build. Reinstall the parent application instead of replacing only the file.The Tool Desk
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- Ergonomic design features more leg room as it hooks onto the steering wheel and positions directly in front of you at a natural level to avoid any strain on the neck, for hours of comfortable use and you don’t need to turn sideways in an awkward position
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- Strong enough to hold a 39 lb concrete block and small enough to stow next to most consoles when not in use
- MADE WITH PRIDE IN THE USA from composite MDF material and protected with an attractive vinyl maple finish laminate
-
The application was copied from another computer
Remove the copied installation and install it from its original legitimate media or installer. -
Several Windows programs are failing, not just the Autodesk application
Check Windows system files with DISM and SFC. -
You are running AutoCAD 2000-era software on Windows 10 or Windows 11
Expect compatibility limits. Autodesk’s current compatibility guidance warns that old unsupported AutoCAD releases may be unstable on newer Windows versions and may not receive fixes. -
The problem started after a graphics or hardware change
Check the application’s own requirements and update the relevant driver, but do not assume a driver package suppliesac1st15.dll.Free tools Windows power users keep installed
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What ac1st15.dll is
ac1st15.dll is the filename of Ac1st15.dll, a 32-bit Autodesk library associated with the ObjectDBX component. ObjectDBX provided shared functionality for older Autodesk products and related CAD applications.
Historical reports associate this library with software including:
- AutoCAD 2000 and AutoCAD 2002
- AutoCAD LT
- Architectural Desktop
- Mechanical Desktop
- Older 3ds Max and VIZ releases
- Some Inventor-era products
- Volo
- Third-party CAD applications built against Autodesk components
The filename alone cannot prove which application installed your copy. Several Autodesk products from the same era may have used related components, and a file from one product release may not be compatible with another.
Some public file inventories identify a copy as Autodesk ObjectDBX and report a version and size, but those records are not Autodesk-published release metadata. Do not use a third-party filename, size, or hash as proof that a replacement file is authentic.
It is not part of Windows
Windows does not normally install ac1st15.dll. It is not a Microsoft runtime, Windows component, DirectX file, or .NET library.
Do not copy it into:
C:WindowsSystem32C:WindowsSysWOW64- Every folder on the computer
A 32-bit application can run on 64-bit Windows through WOW64, but it still needs the correct 32-bit Autodesk DLL in the application’s expected directory. Putting the file in a Windows directory does not repair the Autodesk installation and can create confusing loader problems.
Fix 1: Identify and repair the Autodesk application
This is the most likely solution.
Step 1: Find the program that produces the error
Look at the title bar or text of the error dialog. If it identifies AutoCAD, AutoCAD LT, Architectural Desktop, Mechanical Desktop, 3ds Max, VIZ, Inventor, Volo, or another CAD program, start with that application.
Rank #2
- Made in the USA and designed to be used in a vehicle to support writing and working with a laptop or tablet, making this an ideal tool for the mobile office worker
- Increase productivity by keeping your vehicle organized and efficient with the large work surface and smaller storage compartments located towards the back of the car desk
- The desk is designed to be seat belted into the front passenger seat and is easy to remove or install
- The laptop plate extends the computer another 3 inches from the edge of the work surface
- Size: 15. 15”L x 21. 25”W X 11”H and 18 pounds
If the dialog only names ac1st15.dll:
- Press
Ctrl+Shift+Esc. - Select Task Manager if the small view appears.
- Open the Details tab.
- Look for the program that was starting when the error appeared.
- Right-click it and select Open file location, if available.
- Note the application folder and publisher.
Do not delete the DLL or alter the Windows folders while identifying the owner.
Step 2: Use the application’s repair option
On Windows 11:
- Open Settings.
- Select Apps.
- Select Installed apps.
- Find the Autodesk application.
- Select the three-dot menu beside it.
- Choose Modify, Repair, or Change, depending on what the installer provides.
- Follow the Autodesk setup wizard.
- Restart Windows.
- Start the application again.
On Windows 10:
- Open Settings.
- Select Apps.
- Select Apps & features.
- Select the Autodesk application.
- Choose Modify or Repair, if available.
- Complete the installer.
- Restart Windows and test the program.
Older Autodesk installers may not appear in modern Settings. In that case:
- Press
Windows+R. - Type
appwiz.cpl. - Press Enter.
- Select the Autodesk product.
- Choose Change, Repair, or Modify.
A successful repair should allow the application to start without the missing-file dialog. It should also restore related shared files that may not be obvious from the first error.
Step 3: Reinstall when Repair is unavailable
If there is no repair option, use the original Autodesk installation media or a legitimate installer supplied for that product.
Before uninstalling, make sure you have:
- The original installer or installation disc
- Required license information
- Product serial or activation details, if applicable
- Copies of drawings, templates, plug-ins, and custom settings
Then:
- Open Settings > Apps > Installed apps.
- Locate the affected Autodesk product.
- Select its menu and choose Uninstall.
- Restart Windows if requested.
- Run the original Autodesk installer.
- Install the complete application, including shared components.
- Restart Windows.
- Test the application before restoring optional plug-ins.
If the old application was copied from another computer, reinstall it rather than copying its program folder again. A copied directory may lack shared components, registry entries, configuration, licensing data, or the exact ObjectDBX build required by the executable.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsFix 2: Check antivirus quarantine
A security product may have quarantined or blocked the file. This was historically associated with some older antivirus products, but those reports describe legacy conflicts and should not be treated as a universal current cause.
To check Microsoft Defender on Windows 11:
- Open Settings.
- Select Privacy & security.
- Select Windows Security.
- Select Virus & threat protection.
- Select Protection history.
- Review entries from the time the Autodesk application stopped starting.
- Expand a relevant entry and review the detected path and action.
On Windows 10, open Settings > Update & Security > Windows Security > Virus & threat protection > Protection history.
Only restore a quarantined file when all of the following are true:
- It belongs to your legitimate Autodesk installation.
- Its original path is the application’s own directory or Autodesk shared directory.
- It was not downloaded from a random DLL website.
- The security product’s detection has been reviewed.
- The Autodesk installation itself has not been tampered with.
If the file was unexpectedly replaced or deleted, run a full or offline malware scan instead of immediately restoring it. Do not permanently disable antivirus protection to make the application launch.
After restoring a confirmed original file, start the Autodesk application. If another Autodesk DLL is immediately reported as missing, stop restoring files individually and reinstall the complete application.
Fix 3: Restore the correct DLL build, but only from legitimate media
Manual copying is appropriate only in a narrow situation: you have the exact file from the same legitimate Autodesk product release, installation media, or a verified backup, and you restore it to that product’s original directory.
Rank #3
- Made in the USA and has a 12 inch arm that extends the work tray another 23" from the edge of the desk, providing an extra long "reach" over to the mobile worker for an ergonomic solution.
- Also allows work tray to be extended toward the passenger door, allowing for a standing workspace outside the passenger side of the vehicle
- Increase productivity by keeping your vehicle organized and efficient with the large work surface, hidden storage compartment, and smaller storage compartments located towards the back of the car desk
- The vehicle desk secures to the passenger seat using seat belt and additional cam buckle support system; Easy to install and remove
- Desk Dimensions: 25.25" L x 17" W x 11" H, 19 pounds
Do not use a file from:
- A different AutoCAD release
- Another computer with an unknown installation
- A generic DLL download page
- A forum attachment
- A compressed archive with no product provenance
To restore from original media:
- Insert the Autodesk installation disc or mount the legitimate installer.
- Browse to the installation files.
- Use the installer’s Repair option if available.
- If the installer offers individual component repair, select the ObjectDBX or shared Autodesk component.
- Allow the installer to place the file.
- Restart Windows and test the application.
If you use a verified backup, copy the file only to the application directory where the original installation placed it. Do not place a 32-bit Autodesk DLL in System32 or SysWOW64.
Random DLL downloads are risky because the file may contain malware, belong to a different release, have the wrong architecture, or contain incompatible exports. Even an apparently successful copy does not repair a damaged installer, missing registry configuration, licensing component, or other Autodesk dependency.
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Fix 4: Understand procedure-entry-point errors
A missing-file error and a missing-export error are different.
If Windows says a procedure entry point such as _acFREE@@YIXPAX@Z cannot be found, the loader did find an ac1st15.dll, but that file does not export the function expected by the application. Common explanations include:
- The DLL came from a different Autodesk product or release.
- The application directory contains a mismatched copy.
- A shared Autodesk component was partially removed.
- The program is loading another copy before the intended one.
In this situation, copying another DLL with the same filename is particularly likely to make the problem worse.
Use the application’s Repair option or perform a complete reinstall. If you have multiple old Autodesk products installed, repair the one named in the error first. Avoid adding application directories to the system PATH as a general workaround.
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On Windows 95, Windows 98, and Windows Me, historical Autodesk guidance associated missing shared files with PATH length and AUTOEXEC.BAT configuration. This applies only to those obsolete operating systems.
It is not a suitable general fix for Windows 10 or Windows 11. Do not broadly add random Autodesk folders to the modern Windows PATH.
For a legacy system that genuinely uses AUTOEXEC.BAT:
- Review the Autodesk installation documentation for that exact product.
- Confirm that the Autodesk shared directory is present.
- Check for truncated or conflicting
PATHentries. - Restore the configuration created by the original installer.
- Restart the computer.
- Test the application.
On current Windows, reinstalling the application is safer than reconstructing historical environment variables by hand.
Fix 6: Repair Windows components only when Windows itself is affected
DISM and SFC repair Windows system components. They will not normally reconstruct an Autodesk application DLL, so use them as secondary checks when other Windows files or applications are also failing.
Rank #4
- Made in the USA and has a slide out arm that extends the work tray another 23" from the edge of the desk, providing an extra long "reach" over to the mobile worker for an ergonomic solution.
- Also allows work tray to be extended toward the passenger door, allowing for a standing workspace outside the passenger side of the vehicle
- Increase productivity by keeping your vehicle organized and efficient with the large work surface, hidden storage compartment, and smaller storage compartments located towards the back of the car desk
- The vehicle desk secures to the passenger seat using seat belt and additional cam buckle support system; Easy to install and remove
- Desk Dimensions: 25.25" L x 24" W x 14" H, 19 pounds
First save your work, close applications, and connect the computer to power if it is a portable device.
Run DISM
- Open Start.
- Type
Command Prompt. - Right-click Command Prompt.
- Select Run as administrator.
- Select Yes at the User Account Control prompt.
- Enter:
DISM.exe /Online /Cleanup-image /Restorehealth
- Press Enter.
- Wait for the command to finish.
If DISM reports that the restore operation completed successfully, continue with SFC. If it reports an error, note the message and repair the Autodesk application separately rather than treating DISM as a source for ac1st15.dll.
Run System File Checker
In the same elevated Command Prompt, enter:
sfc /scannow
Press Enter and wait until verification reaches 100 percent. Restart Windows afterward, then test the Autodesk application.
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If SFC reports that it repaired files, retest the application. If it reports that it found no integrity violations, the missing Autodesk DLL still needs to be repaired through the Autodesk installer. If it cannot repair some files, review the DISM result and Microsoft’s current System File Checker guidance.
Repeatedly running SFC and DISM without knowing what changed can waste time when the damaged file belongs to Autodesk. Outbyte PC Repair can show what it identifies during a scan, while its repair functions require the full version; it is optional, and reinstalling the Autodesk program remains the definitive fix for this application DLL.
Fix 7: Do not use regsvr32 for this DLL
Do not run:
regsvr32 ac1st15.dll
regsvr32 is for self-registering OLE and ActiveX components that expose a registration entry point such as DllRegisterServer. A normal application or runtime DLL does not necessarily provide that function.
If you run the command against a DLL without the required entry point, Windows may report that the module was loaded but DllRegisterServer was not found. That does not mean the file is repaired or that registration was required.
Use the Autodesk installer to restore application files and configuration. Do not register the file simply because its name ends in .dll.
Fix 8: Check Windows compatibility and isolation
AutoCAD 2000-era software predates current 64-bit Windows behavior, security controls, installer rules, and filesystem changes. Windows 10 or Windows 11 may run some older applications, but compatibility is not guaranteed.
Try the built-in compatibility troubleshooter only after repairing the installation:
- Right-click the Autodesk program’s shortcut.
- Select Properties.
- Open the Compatibility tab.
- Select Run compatibility troubleshooter.
- Follow the prompts.
- Test the application with the recommended settings.
Compatibility mode alone will not replace a missing or mismatched DLL.
If the program remains unstable, the practical choices are:
Best Value
- Made in the USA and has a slide out arm that extends the work tray another 23" from the edge of the desk, providing an extra long "reach" over to the mobile worker for an ergonomic solution.
- Also allows work tray to be extended toward the passenger door, allowing for a standing workspace outside the passenger side of the vehicle
- Increase productivity by keeping your vehicle organized and efficient with the large work surface, hidden storage compartment, and smaller storage compartments located towards the back of the car desk
- The vehicle desk secures to the passenger seat using seat belt and additional cam buckle support system; Easy to install and remove
- Desk Dimensions: 25.25" L x 24" W x 14" H, 19 pounds
- Move to a currently supported Autodesk release.
- Use an appropriately licensed older Windows installation.
- Run the legacy application in an isolated virtual machine.
- Keep the legacy environment separate from normal browsing and current work.
Autodesk’s compatibility guidance should be checked before relying on an unsupported release for important production work.
Fix 9: Update a relevant device driver only when evidence points there
A graphics driver can affect an old CAD program’s display or stability, but a driver update is not a normal source for ac1st15.dll. Update drivers only if the Autodesk application also reports display corruption, hardware initialization errors, or a problem that began immediately after a graphics change.
To check the graphics driver:
- Right-click Start.
- Select Device Manager.
- Expand Display adapters.
- Right-click the graphics device.
- Select Properties.
- Open the Driver tab.
- Note the provider and driver date.
- Use Update Driver or obtain the driver from the computer or graphics-device manufacturer.
- Restart Windows and test the application.
Do not use Device Manager to replace ac1st15.dll. If the driver update fails, use Roll Back Driver from the same tab when that option is available, or reinstall the manufacturer’s known-good driver.
Manually hunting through driver versions and guessing which of several devices is stale is tedious; Outbyte Driver Updater can identify drivers during its free scan, while driver installation requires the full version. It is optional and does not replace repairing the Autodesk installation that owns ac1st15.dll.
Prevention
After the application works again:
- Keep the original Autodesk installer or installation media with the product records.
- Back up the application’s project files, templates, custom profiles, and licensing information.
- Do not copy an Autodesk program directory between computers as a substitute for installation.
- Record which Autodesk product and release uses the DLL.
- Review antivirus quarantine when an application file disappears.
- Avoid registry cleaners and DLL “fixer” utilities.
- Do not place application DLLs in Windows system directories.
- Keep unsupported Autodesk software isolated when possible.
- Test a repaired installation before restoring third-party plug-ins.
FAQ
Is ac1st15.dll a Windows file?
No evidence supports treating it as a Windows system file. It is associated with Autodesk ObjectDBX and legacy Autodesk applications.
Which Autodesk program installed it?
The filename alone cannot identify the exact parent product. Historical reports associate it with AutoCAD-era products and several related Autodesk or third-party CAD applications. Identify the executable that displays the error, then repair that application.
Should I download ac1st15.dll?
No. Random DLL downloads can provide malware, the wrong architecture, or an incompatible build. Use the original Autodesk media, a verified backup, or the application’s official repair and reinstall process.
Can I copy it to System32?
No. The correct location is normally the Autodesk application or shared Autodesk directory. System32 and SysWOW64 are not general-purpose storage locations for application DLLs.
Will Visual C++ Redistributable, DirectX, or .NET fix it?
There is no evidence that those packages supply ac1st15.dll. Install them only when the specific Autodesk application separately requires them.
Why does the file exist but Windows still report an error?
It may be in the wrong directory, blocked, damaged, or from an incompatible Autodesk release. A missing procedure entry point strongly indicates a version mismatch. Repair or reinstall the parent application.
Can SFC restore ac1st15.dll?
Normally no. SFC repairs protected Windows system files, not Autodesk application files. Use it only when there are broader Windows corruption symptoms.
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When should I stop troubleshooting?
Stop replacing individual DLLs when the application reports additional missing files, procedure-entry errors, repeated crashes, or licensing failures. At that point, reinstall the complete application or move it to an isolated, appropriately licensed legacy environment.
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