Start with this diagnostic checklist
Before replacing anything, record:
- Which program shows the error: an Access database, accounting tool, database utility, VB6 application, or another legacy program
- When it appears: during Windows startup, when opening the program, or when opening a particular
.mdbfile - What changed: an uninstall, antivirus detection, disk cleanup, Windows Update, migration, or failed application update
- Where the file is expected: the application’s installation folder,
System32, orSysWOW64 - Whether the program is 32-bit: most older Jet-based applications are
- The exact message: “not found,” “missing or corrupted,” or “The specified module could not be found”
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Do not begin by downloading a0004075.dll from a random DLL website. A downloaded copy can have the wrong architecture or version, can be modified, and may leave the real missing dependency or damaged application installation untouched.
What a0004075.dll is
a0004075.dll is reported as Microsoft (R) Red ISAM, part of Microsoft (R) Jet. Jet Red is Microsoft’s legacy database engine component used by Access and applications that work with older .mdb databases.
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Microsoft documentation identifies the canonical 32-bit ISAM driver for Access 3.0 and Access 97 formats as Msrd3x40.dll, also commonly written as MSRD3X40.DLL. Public file inventories associate a0004075.dll with that component, but Microsoft documentation does not establish a0004075.dll as the normal installed Windows filename. It may be an installer name, an archived copy, or a renamed copy.
That distinction matters. The filename in the error may not be the filename Windows normally uses. Copying a file with the matching name into a system directory is therefore not a reliable repair.
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Jet Red is also not the same thing as Jet Blue. Jet Blue is the unrelated Extensible Storage Engine used by other Microsoft products. Microsoft’s explanation of that distinction is available in its Extensible Storage Engine documentation.
The file is not inherently a malware name. Malware can use any filename, however, so a copy found outside the application’s installer or Windows’ protected component store should be checked before it is restored.
Fix 1: Identify and repair the application first
If only one old program fails, repair that program before changing Windows. This is the most likely solution when the problem began after uninstalling software, cleaning an old installation, moving the program to another computer, or interrupting an update.
Repair a Windows-installed desktop program
- Close the affected program.
- Open Start and search for Control Panel.
- Select Programs and then Programs and Features.
- Select the application that displays the
a0004075.dllerror. - Right-click it and choose Repair or Change.
- Follow the installer’s prompts.
- Restart Windows.
- Launch the application and open the database or document that previously failed.
On Windows 11, some programs also expose a repair command through Settings:
- Open Start > Settings.
- Select Apps > Installed apps.
- Find the affected program.
- Select the three-dot menu beside it.
- Choose Advanced options if available.
- Select Repair.
- If Repair does not resolve the error, return to the same screen and use Reset only if you have the program’s settings and data backed up.
Microsoft documents these application repair paths in its repair apps and programs guidance.
If the program has no repair option, uninstall it from Apps > Installed apps or Programs and Features, restart, and reinstall it from the original vendor media or a verified download from the application publisher. Do not remove the application’s data folder unless the vendor’s instructions specifically require it.
Check the application folder
If the program is portable or was installed from older media, open its installation folder and look for its database engine files. Common locations include:
C:Program Files...C:Program Files (x86)...- A folder beneath
C:Users<your name>AppData - A folder selected by the program’s original installer
Do not assume that a file in the application folder should be copied into System32 or SysWOW64. An application-local dependency may need the installer’s registry entries, configuration files, supporting DLLs, and exact matching build.
A repair worked if the program starts normally and can perform the database operation that caused the error. If the same error returns immediately, continue with the checks below rather than copying an isolated DLL.
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Fix 2: Check Windows Security for quarantine
Antivirus software may have quarantined a copy belonging to the application. This is especially relevant when the error appeared immediately after a scan or after an application update.
- Open Start and search for Windows Security.
- Select Virus & threat protection.
- Choose Protection history.
- Review recent detections for the affected application folder.
- Expand a detection to inspect its path, name, and action.
- Restore the file only when you have verified that it came from the legitimate application installer or publisher.
- Repair or reinstall the application afterward if Windows Security removed supporting files.
Microsoft warns that restoring a genuinely malicious file can expose the device. If the file came from an unofficial DLL source, do not restore it. Remove that copy and reinstall the application from legitimate installation media.
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Protection History does not retain events indefinitely, so an older quarantine event may no longer be visible. If the event is gone and the application still fails, reinstalling the application is safer than trying to reconstruct the deleted file manually.
A successful repair means Windows Security no longer removes the application’s files and the program starts after a restart. If a newly installed copy is quarantined again, stop restoring it and investigate the detection before proceeding.
Fix 3: Repair Windows component files with DISM and SFC
Use Windows repair commands when:
- More than one application reports missing or damaged Microsoft components
- The error involves a file under a Windows system directory
- Windows Update or disk corruption preceded the problem
- Application repair did not help
- The system has other unexplained file or servicing errors
Open an elevated Command Prompt:
- Open Start.
- Type Command Prompt.
- Right-click Command Prompt and select Run as administrator.
- Approve the User Account Control prompt.
- Run this command:
DISM.exe /Online /Cleanup-Image /RestoreHealth
Wait for it to finish. DISM repairs the Windows component store used by system-file recovery. When it completes, run:
sfc /scannow
Let the scan reach 100 percent. Then restart Windows.
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If SFC reports that it repaired files, retry the affected application. If it reports that it found corrupt files but could not repair some of them, restart and run the same sequence once more. If DISM itself fails, install pending Windows Updates, restart, and repeat the commands.
Outbyte PC Repair can reduce the manual work of hunting through repair results and repeating SFC or DISM without knowing what changed; its free scan shows what it identifies, while repair is handled by the full version. It is optional, and reinstalling the specific legacy application remains the definitive fix when that application owns the missing component.
Install pending Windows Updates
- Open Start > Settings.
- Select Windows Update.
- Choose Check for updates.
- Install all available updates.
- Restart when prompted.
- Return to Windows Update and check again until no further updates are offered.
- Test the affected program.
If the problem began immediately after a particular update, review Microsoft’s release information and Windows recovery options before replacing system files manually.
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Fix 4: Check 32-bit and 64-bit compatibility
Jet has no 64-bit version. A 32-bit application must use 32-bit database components even when Windows 11 or Windows 10 is 64-bit.
On 64-bit Windows:
C:WindowsSystem32normally contains 64-bit system filesC:WindowsSysWOW64normally contains 32-bit system files- A 32-bit program is normally installed beneath
C:Program Files (x86)
The names are confusing, but do not use the folder name alone to decide what to copy. Do not place a 32-bit DLL in System32 to make a 64-bit process load it. That cannot turn a 32-bit Jet component into a 64-bit one.
To check whether the affected program is 32-bit:
- Start the program if it opens far enough to display its menus.
- Open Task Manager with
Ctrl+Shift+Esc. - Select Details.
- Locate the program’s executable.
- Right-click the column headings and enable Select columns if needed.
- Look for an architecture indicator when available, or identify the executable’s installation path.
- Confirm the architecture with the application vendor if the result is unclear.
A legacy Access or VB6 program is commonly 32-bit, but the application’s documentation is the authority. If the program is 32-bit, installing only an x64 database package will not repair a missing 32-bit Jet dependency.
Fix 5: Do not substitute ACE without checking the application
Microsoft’s Access Database Engine is a separate database connectivity product. Its 2016 Redistributable offers x86 and x64 packages, but it is not a guaranteed drop-in replacement for a program that specifically requires Jet Red, Jet 3.x, old DAO, or Access 97 behavior.
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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Install it only when the application vendor explicitly says that the program requires it. Use Microsoft’s official Access Database Engine 2016 Redistributable page, and match the package to the consuming application, not simply to the bitness of Windows.
The x86 installer is named accessdatabaseengine.exe. The x64 installer is named accessdatabaseengine_X64.exe. Installing the wrong architecture can fail to help and may conflict with existing Office or Access components.
Before installing:
- Close Office, Access, and the affected application.
- Confirm the application’s required provider with its vendor documentation.
- Check whether Office is 32-bit or 64-bit.
- Download only from Microsoft’s page.
- Select the package that matches the application.
- Restart Windows.
- Test the original program and database.
Microsoft states that ACE 2016 support ends on October 14, 2025. It also distinguishes Jet 4.0 from later MDAC releases, which do not include Jet components. Do not assume that a current ACE installer recreates every behavior of the legacy Jet provider.
If the application still reports a0004075.dll after an approved ACE installation, remove ACE from your list of assumptions and return to application repair or vendor support.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsFix 6: Check whether the Windows installation or user profile is damaged
If application repair, Defender review, DISM, SFC, and architecture checks do not resolve the problem, determine whether the failure is system-wide or limited to one Windows profile.
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Test with a new local account
- Open Start > Settings.
- Select Accounts > Other users.
- Choose Add account.
- Select I don’t have this person’s sign-in information.
- Choose Add a user without a Microsoft account.
- Create a temporary local account.
- Sign out and sign in to that account.
- Test the application, if its installation and data are available to the account.
If the program works under the new account, the original profile may have damaged settings, permissions, or path configuration. Do not immediately delete the old profile. Move only necessary user data after confirming the result and checking the application’s data requirements.
Use System Restore
Use System Restore when the failure began after a known application, driver, or Windows change and a suitable restore point exists.
- Open Start and search for Create a restore point.
- Open the result.
- Select System Restore.
- Choose a restore point dated before the failure.
- Review the affected programs and drivers.
- Back up important work.
- Complete the restore and restart.
System Restore changes system files, settings, drivers, and installed programs. It does not normally remove personal files, but important data should still be backed up first. Microsoft describes these options in its Windows recovery documentation.
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On Windows 11, Microsoft provides a repair reinstall option on supported systems:
- Open Start > Settings.
- Select System > Recovery.
- Find Fix problems using Windows Update.
- Select Reinstall now.
- Follow the prompts.
This reinstalls the current Windows version while preserving apps, files, and settings according to Microsoft’s recovery guidance. If the option is unavailable, use the recovery instructions for your Windows installation rather than deleting system DLLs manually.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why regsvr32 usually does not fix this error
Do not run:
regsvr32 a0004075.dll
regsvr32 is intended for self-registering COM and ActiveX libraries. A database-engine runtime DLL is not automatically a COM server that should be registered. Microsoft’s ActiveX registry documentation describes the COM registration model, but it does not establish that a0004075.dll or MSRD3X40.DLL should be registered with regsvr32.
Registering the wrong file can produce another error and distract from the actual cause. Use regsvr32 only if the application vendor explicitly documents that exact command for that exact file and architecture.
Why manual copying is usually unsafe
Manual copying fails frequently because:
- The file may be the wrong architecture
- The file may not match the application’s expected build
- A dependent DLL may also be missing
- The application may require installer registry entries
- Windows may be using a canonical filename different from the error filename
- Copying into protected Windows folders can overwrite system components
- The downloaded file may be malicious or modified
The narrow exception is restoring a verified file from the same application’s original installer or a known-good backup into that application’s own folder, after confirming the exact architecture and version with the vendor. Even then, running the application’s repair or reinstall process is preferable.
Fix 7: Update drivers only when broader symptoms point there
A missing Jet component is not normally a graphics, chipset, or storage-driver problem. Do not use Device Manager as the first response to a single a0004075.dll error.
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Check drivers only when the application failure began with broader hardware symptoms, Windows crashes, storage errors, or a recent device change:
- Right-click Start.
- Select Device Manager.
- Expand the relevant category, such as Storage controllers, IDE ATA/ATAPI controllers, or System devices.
- Right-click the affected device.
- Choose Properties and review the General and Driver tabs.
- Use Update driver > Search automatically for drivers.
- Restart Windows and test the application.
Do not uninstall a storage or chipset device merely because the DLL error appears. Obtain specialized drivers from the computer or device manufacturer when Windows cannot find a suitable update.
Outbyte Driver Updater can reduce the pain of hunting through many hardware entries and guessing which driver is stale; its free scan identifies what it finds, while driver installation is handled by the full version. It is optional, and it will not replace the application repair needed when Jet itself is the missing dependency.
If the error persists
At this point, collect the details a vendor technician needs:
- The application name and exact release
- The full error text
- Whether the application is 32-bit
- The application installation path
- Whether the file was found in the application folder,
System32, orSysWOW64 - The result of application repair
- The result of DISM and SFC
- Any Defender detection
- The Windows version and recent changes
- Whether the program uses Access 97, Jet 3.x, Jet 4.0, or another provider
Contact the application publisher with that information. The durable fix may be a vendor update, a compatibility change, a supported replacement, or migration from the obsolete Jet provider.
If malware or severe Windows corruption is suspected, perform a full Microsoft Defender scan and back up important data before considering a clean Windows installation. A clean reinstall is a last resort, not the first response to an isolated legacy application error.
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FAQ
Is a0004075.dll a Windows system file?
It is associated with Microsoft Jet, but the name a0004075.dll is not established by Microsoft documentation as the normal canonical installed filename. Microsoft documentation refers to Jet ISAM files such as Msrd3x40.dll.
Is it the same as MSRD3X40.DLL?
Public file metadata strongly associates the two names, but Microsoft documentation does not confirm that they are always interchangeable. Treat the error as evidence of a missing or damaged Jet-related dependency, then repair the owning application.
Should I download the DLL?
No. Random DLL downloads can provide the wrong file, architecture, or version and can introduce malware. Use the application’s original installer, the publisher’s verified installer, Windows Update, and Microsoft’s repair tools.
Will Access Database Engine fix it?
Not necessarily. ACE is not guaranteed to replace Jet Red or preserve old Jet 3.x and Access 97 behavior. Install it only when the application vendor specifically requires it, using the architecture that matches the application.
Why does “The specified module could not be found” appear when the file exists?
Windows may be unable to load a dependency required by the named DLL. Check the application installation and repair it rather than assuming the displayed filename is the only missing file.
Should I copy the file to both System32 and SysWOW64?
No. That can place an incorrect file in protected system directories and does not solve architecture or dependency problems. Repair the application or Windows component through its supported installer and recovery tools.
Can this filename indicate malware?
The filename itself is not proof of malware. Verify its location and origin, review Windows Security Protection History, and restore only a confirmed-safe file from the legitimate application or Microsoft source.
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