Fix: ERROR_UNSUPPORTED_COMPRESSION 618 (0x26A)

The ERROR_UNSUPPORTED_COMPRESSION Windows system error, with code 618 (0x26A), arises when the compression format for a file is not supported by the OS. The error message reads, The specified compression format is unsupported.

This can be due to issues with the said file, incorrect/unsupported format, corrupted system files, and the presence of conflicting apps.

Before you proceed to the solutions, reboot the computer, install all pending Windows updates, and try redownloading the file from the original source and then verifying whether it still throws the error!

How can I fix ERROR_UNSUPPORTED_COMPRESSION?

1. Check for issues with the file or format

When only a single file is triggering ERROR_UNSUPPORTED_COMPRESSION 618 (0x26A), check the format and make sure that it’s compatible with Windows.

If it’s unsupported, use a top-rated file compression software since these add support for a wide array of formats and allow quick file access, helping you get rid of the system error.

2. Take full ownership of the file

1. Right-click on the affected file, and select Properties.
2. Go to the Security tab, and click on Advanced.
3. Click the Change button.
4. Type Everyone in the text field, click on Check Names, and then on OK.
5. Tick any checkboxes available on this window, and then click on Apply and OK to save the changes.
6. Now, click the Edit button.
7. Click on Add.
8. Again, type Everyone in the available field, click on Check Names, and then OK.
9. Select the newly added entry, and tick the checkbox for Full control.
10. Click Apply and OK to save the changes, then restart the PC and check for improvements.

The ERROR_UNSUPPORTED_COMPRESSION system error is also sometimes caused by missing permissions. In this case, taking full ownership of the file will do the trick!

3. Repair the corrupt 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 individually and hit Enter after each: DISM /Online /Cleanup-Image /CheckHealth DISM /Online /Cleanup-Image /ScanHealth DISM /Online /Cleanup-Image /RestoreHealth
4. Now, run this command for the SFC scan: sfc /scannow
5. Finally, reboot the PC to apply the changes.

Corrupted system files are also found to cause system errors 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!

4. Uninstall conflicting third-party apps

1. Press Windows + R to open Run, type appwiz.cpl in the text field, and hit Enter.
2. Select any app installed around the same time the issue first appeared, and click on Uninstall.
3. Follow the on-screen instructions to complete the process.
4. Restart the computer and check for improvements.

If a quick removal doesn’t fix ERROR_UNSUPPORTED_COMPRESSION, the app may have left behind files or Registry entries that are still conflicting with Windows. To get rid of all these, I recommend using an effective software uninstaller!

5. Reinstall Windows

When nothing else works, the last option is to reinstall Windows. Remember, there’s a possibility of data loss here. So, it’s best that you move any critical files to an external drive beforehand.

To reinstall Windows, go to Microsoft’s official website > download the Media Creation Tool > use it to create a bootable Windows USB > then change the boot order to the flash drive > run the Windows setup and install Windows.

Since ERROR_UNSUPPORTED_COMPRESSION is a software-based issue, reinstalling Windows will, in all likelihood, fix things, given that the OS supports the file format. Otherwise, you will have to install a dedicated software.

Before you leave, discover the common Windows problems and expert fixes, and prevent such errors from reappearing!

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