What the avmcoxp.dll error means
Common messages include:
- “The program can’t start because avmcoxp.dll is missing from your computer.”
- “Error loading avmcoxp.dll. The specified module could not be found.”
- “Failed to load avmcoxp.dll.”
- “avmcoxp.dll is either not designed to run on Windows or it contains an error.”
- “The procedure entry point could not be located in the dynamic link library avmcoxp.dll.”
avmcoxp.dll is an AVM ISDN-Controller NDIS WAN CoInstaller component, not a normal Windows runtime such as Visual C++, DirectX, or .NET. The safest fix is to identify the AVM ISDN controller or legacy software that requested it, then repair or reinstall its complete driver package.
Do not download the DLL by itself, copy it into System32, or run regsvr32 as a first response. A standalone file can be malicious, built for the wrong architecture, or unable to work because the real problem is a missing driver or dependency.
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The 60-second fix
- Open Device Manager by right-clicking Start and selecting Device Manager.
- Expand Network adapters and look for an AVM ISDN controller or a device with a warning icon.
- If you still use the hardware, obtain the complete driver package from the original AVM media or AVM’s official legacy archive.
- Match the package to the Windows edition, hardware model, and system architecture.
- Uninstall the damaged device and its driver, restart Windows, and install the complete package again.
- Check Device Manager after the restart.
If you no longer own or use an AVM ISDN controller, uninstalling the obsolete AVM software is usually the correct fix. Restoring an old driver component for hardware that is gone can leave unnecessary startup entries and failed device-installation requests.
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What avmcoxp.dll does
AVM used this component with legacy ISDN-controller driver packages, including the B1 PCI family and related AVM or Fritz.Card products. The associated NDIS WAN CAPI driver allowed an ISDN controller to work through Windows networking and Remote Access Service.
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The “co-installer” part is important. Microsoft defines a driver co-installer as a DLL called during device installation through an INF file. That makes avmcoxp.dll an installation and driver component, not a general-purpose application library.
The file may be present inside an AVM driver package, the Windows DriverStore, or a component-store copy associated with an AVM INF package. Its exact location varies by Windows version and installation method.
Why the error appears
The usual causes are:
- An AVM controller driver installation was interrupted or damaged.
- The device was removed but an old startup program or driver entry remains.
- A 32-bit and 64-bit driver package was mixed.
- Windows component or DriverStore files became corrupted.
- Antivirus software quarantined the file.
- Disk cleanup or a system-image restoration removed part of the package.
- A Windows upgrade exposed an incompatible legacy driver.
- The DLL exists, but a dependency it needs is missing.
A message saying “the specified module could not be found” does not always mean the named DLL itself is absent. Windows may be unable to load one of its dependencies.
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This is the most likely solution when the hardware is still installed.
Identify the device
- Press Windows key + X.
- Select Device Manager.
- Expand Network adapters.
- Look for AVM ISDN-Controller, B1 PCI, Fritz.Card, or an Unknown device with a warning icon.
- Right-click the device and select Properties.
- Check the General, Driver, and Details tabs. The Hardware Ids entry can help identify the exact controller.
Use the original AVM installation media or an AVM-provided legacy package. Do not combine a DLL from one release with an INF or driver from another.
Remove the damaged installation
- In Device Manager, right-click the AVM device.
- Select Uninstall device.
- If Windows shows Attempt to remove the driver for this device, select it when you intend to remove the damaged package.
- Select Uninstall.
- Restart Windows.
If the device is not visible, select View from Device Manager’s menu and enable Show hidden devices. Remove only the stale AVM entry you have identified.
Install again
Run the AVM installer from trusted original media or the official AVM archive. If there is no installer:
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- Open Device Manager.
- Right-click the AVM or unknown device.
- Select Update driver.
- Choose Browse my computer for drivers.
- Select the extracted AVM driver folder.
- Enable Include subfolders.
- Select Next.
Restart when installation finishes. In Device Manager, the warning icon should be gone, and the device’s Device status should say that it is working properly.
Driver architecture matters. Use an x86 package on 32-bit Windows and an x64 package on 64-bit Windows. A compatibility mode setting cannot create a missing kernel driver, and a driver listed by a download page as supporting a newer Windows version is not proof that it works on that version.
When manually hunting through old packages, it is easy to select the wrong controller or architecture. Outbyte Driver Updater can scan for outdated or mismatched drivers; its free scan shows what it finds, while driver installation is handled by the full version. For this specific AVM hardware, reinstalling the correct original package remains the definitive fix.
Fix 2: Remove obsolete AVM software
Use this path if the hardware is no longer connected or required.
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- Select Apps, then Installed apps.
- Search for AVM, Fritz.Card, B1, ISDN, or CAPI software.
- Select the matching entry and choose Uninstall.
- Restart Windows.
Then check for a stale device:
- Open Device Manager.
- Select View → Show hidden devices.
- Expand Network adapters and other relevant categories.
- Right-click an obsolete AVM entry.
- Select Uninstall device.
- Restart again.
If an old application still requests avmcoxp.dll after removal, check its shortcut, scheduled tasks, and startup entries. Do not restore the DLL merely to keep obsolete software launching.
Fix 3: Repair Windows component files
Use Windows repair commands when the AVM component was integrated into Windows or when other system files also appear damaged. These commands do not install a missing third-party AVM driver package on every system.
- Right-click Start.
- Select Terminal (Admin) or Command Prompt (Admin).
- Approve the User Account Control prompt.
- Run this command:
DISM.exe /Online /Cleanup-Image /RestoreHealth
Wait for it to finish. Then run:
sfc /scannow
Restart Windows after both commands complete. Try the AVM installer or Device Manager installation again.
DISM repairs the Windows component store. SFC checks protected Windows files. If SFC reports that it repaired files, test the original program or device. If it reports that it could not repair everything, reinstall the AVM package rather than copying avmcoxp.dll manually.
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Repeatedly running SFC and DISM without knowing which driver package is missing rarely solves a legacy-device installation. Outbyte PC Repair can show what its free scan identifies, while repairs are performed by the full version. It is optional, and it does not replace reinstalling the correct AVM driver.
Fix 4: Check antivirus quarantine
Security software can remove or quarantine an old driver component.
In Windows Security:
- Open Start and search for Windows Security.
- Select Virus & threat protection.
- Select Protection history.
- Look for an event involving
avmcoxp.dll, an AVM installer, or the AVM driver directory. - Open the event and inspect the original path and detection details.
Restore the file only if all of the following are true:
- It came from trusted AVM installation media or an official AVM package.
- The original location matches the AVM driver installation.
- The package has a valid digital signature where one is expected.
- You still need the associated hardware.
Do not restore a file obtained from a DLL download sites page. If the file is suspicious, leave it quarantined, run a full Microsoft Defender scan, and reinstall the driver from trusted media.
Fix 5: Use System Restore after a recent change
If the problem began immediately after a driver update, cleanup operation, Windows change, or system-image restoration, System Restore may roll back the driver and registry state.
- Press Windows key + R.
- Type:
rstrui.exe
- Press Enter.
- Choose a restore point from before the error began.
- Select Next, review the affected programs, and select Finish.
- Allow Windows to restart.
System Restore does not delete personal files, but it can remove drivers and applications installed after the selected restore point. Reinstall the AVM package afterward if necessary.
Why you should not use regsvr32
regsvr32 registers DLLs that expose registration entry points such as DllRegisterServer. A driver co-installer is normally invoked by the device’s INF installation process.
Running commands such as these is therefore not a general repair:
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regsvr32 avmcoxp.dll
regsvr32 /u avmcoxp.dll
They may produce another error, change nothing, or encourage copying the file into an unsafe directory. Windows DLL search behavior also means that placing an arbitrary DLL in a searched folder can create loading conflicts and security risk.
FAQ
Is avmcoxp.dll a Windows system DLL?
No. It is associated with AVM ISDN-controller driver software. Windows 7-era installations could include a corresponding AVM controller driver, but that does not make every build a Windows core file.
Do I need Visual C++ or DirectX?
Not as the primary fix. This is a legacy AVM driver component, so repair the AVM controller package or remove obsolete AVM software first.
Can I download avmcoxp.dll by itself?
You should not. A standalone file may be malicious, incompatible, or missing dependencies. Obtain the complete driver package from original AVM media or the official AVM archive.
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Why does Windows say the module is missing when the file exists?
A dependency may be missing, the file may have the wrong architecture, or the driver installation may be incomplete. Reinstall the complete matching package rather than copying another DLL.
Will it work on Windows 10 or Windows 11?
That cannot be assumed. AVM’s documented controller support covers older Windows generations, and modern Windows versions may not support the required legacy hardware or kernel driver. Check the exact controller and package before attempting installation.
What information should I collect if nothing works?
Record the full error text, the executable that displays it, the AVM hardware model, Windows edition and build, whether Windows is 32-bit or 64-bit, and the complete path mentioned in the error. This distinguishes a missing driver from an obsolete program that is still starting automatically.
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