The most common reason is that it contains a mounted Windows image (WIM/VHD) that was not unmounted properly, with other possible causes including TrustedInstaller owning it, encryption, or system processes still running.
1. Delete Directory via Command Prompt
If you want a method that’s very likely to work, boot into the Advanced Options menu and delete the mountUUP directory from an elevated Command Prompt before Windows mounts anything from it. Note: Opening an elevated CMD from Advanced Options is necessary because you need to do this before Windows has a chance to lock files in the mountUUP folder.
2. Giving Yourself Full Control of the folder
Often, the issue is caused by permissions. If you’d rather not force-delete the folder, you can take ownership and give your account full control, then delete it normally.
3. Unmount and Clean the .WIM or .VHD files first
If the methods above didn’t work, the folder may contain a .wim or .vhd file that’s currently mounted. In that case, Windows will keep the folder in use and block deletion. You can fix this by running a DISM command to unmount and clean up any mounted images. Follow these steps: Another reliable option is to boot in Safe Mode without Networking. This starts Windows with only essential services, so any .wim files in mountUUP won’t be used by the system. Note: Use Safe Mode without Networking to prevent Windows Update components from accessing files in the mountUUP folder. Note: These steps work on Windows 8.1, Windows 10, and Windows 11.
5. Remove mountUUP from the list of Protected Folders
A less common cause is Windows Security (Defender) protecting the mountUUP folder through Controlled folder access. While it’s protected, you won’t be able to delete it. To fix this, remove mountUUP from the Protected folders list, then delete it normally.
