ERROR_ASSERTION_FAILURE 668 (0x29C) [Solved]

The ERROR_ASSERTION_FAILURE Win32 system error, with code 668 (0x29C), appears when applying attributes to a file or sometimes at startup. This happens due to missing permissions, corrupted system files, issues with Hyper-V, and broken Microsoft Visual C++ Redistributables.

The message for Error Code 668 reads, An assertion failure has occurred.

Before you proceed to the solutions, restart the PC, install all pending Windows updates, and make sure you are running the latest BIOS version. For most of you, these basic checks will do the trick!

How can I fix the ERROR_ASSERTION_FAILURE system error?

1. Disable the Read-only file attribute

1. Right-click on the file throwing the error while applying attributes, and select Properties.
2. In the General tab, untick the checkbox for Read-only.
3. Click Apply and OK to save the changes.
4. Finally, select the Unblock option in the file’s properties and check for improvements.

For 3 out 5 users facing ERROR_ASSERTION_FAILURE 668 (0x29C) An assertion failure has occurred while unblocking a file, disabling the read-only attributed got things up and running in no time!

2. Repair the system files

1. Press Windows + S to open Search, type Command Prompt, and click on Run as administrator.
2. Click Yes in the UAC prompt.
3. Paste the following DISM commands one after another and hit Enter after each: DISM /Online /Cleanup-Image /CheckHealth DISM /Online /Cleanup-Image /ScanHealth DISM /Online /Cleanup-Image /RestoreHealth
4. Run this command for the SFC scan: sfc /scannow
5. Once done, reboot the PC to apply the changes.

When the system files are corrupted, you are likely to encounter Error Code 668 ERROR_ASSERTION_FAILURE in Windows. To fix this, run the DISM (Deployment Image Servicing and Management) and SFC (System File Checker) scans, which will replace all affected files with their cached copies!

3. Re-enable Hyper-V

1. Press Windows + S to open Search, type Turn Windows features on or off, and click on the relevant result.
2. Uncheck the Hyper-V option here, click OK to save the changes, and restart the PC.
3. When the PC boots up, open Windows Features, re-enable Hyper-V, and again perform a restart to apply the changes.

If you are getting the ERROR_ASSERTION_FAILURE message on a virtual machine set up using Hyper-V, disabling and then enabling Hyper-V will fix things.

4. Repair/reinstall Visual C++ Redistributables

1. Press Windows + R to open Run, type appwiz.cpl in the text field, and hit Enter.
2. Select any Microsoft Visual C++ Redistributable entries listed here, and click on Change.
3. Click the Repair button and wait for the process to complete.
4. Similarly, repair any other Visual C++ redistributable packages on the PC.

When you are getting the Assertion failed error in Microsoft Visual C++ Runtime Library on startup, it’s likely due to corruption in the installed package. In case repairing them doesn’t work, uninstall the packages and get fresh copies from Microsoft’s official website!

5. Perform a system restore

1. Press Windows + S to open Search, type Create a restore point, and click the relevant result.
2. Click on System Restore.
3. Select the Choose a different restore point entry, if available, and click Next.
4. Pick the oldest restore point from the list or one created before you first encountered the system error, and click Next.
5. Verify the restore details, click Finish, and confirm the change.
6. Wait for the restore to complete. It usually takes 15-45 minutes.

If nothing else works, performing a system restore will fix ERROR_ASSERTION_FAILURE and prevent those annoying pop-ups from reappearing!

As you can see, Error Code 668: An assertion failure has occurred is a software-based error that can be resolved with simple solutions and workarounds. In case you can’t get rid of it, contact Microsoft support for more help.

Before you leave, learn about common Windows 11 errors and expert solutions to prevent such issues from reappearing!

For any queries or to share which fix worked for you, drop a comment below.