Case 1: Windows System Restore Error Code 0x80070091

Solution 1: Rename WindowsApps folder to fix system restore error 0x80070091

Step 1. Press Windows key and R together to open Run dialogue. Then type msconfig in Run box and click OK to open System Configuration.
Step 2. Click Boot tab on the System Configuration window. Then select "Safe boot" under Boot options and click OK button. If you are prompted by computer, click Restart to reboot computer. Before starting, save any open files and close all programs.
Step 3. Restart computer and system will boot into Safe Mode automatically.
Step 4. Right-click the Start menu and select Command Prompt (Admin) to open Command Prompt window.
Step 5. Type following commands in Command Prompt and press Enter key after each command:
cd C:\Program Files
takeown /f WindowsApps /r /d Y
icacls WindowsApps /grant "%USERDOMAIN%%USERNAME%":(F) /t
attrib WindowsApps -h
rename WindowsApps WindowsApps.old
Step 6. Open System Configuration window again, unselect Safe boot and click OK button.
Step 7. Restart computer and try system restore to check if the error code is fixed.

Solution 2: Restore system in Windows Recovery Environment

Step 1: Click Start menu and select Settings to open Windows Settings where you should select Update & security.
How to fix error code 0x80070091 in Windows 10

Step 2: Choose Recovery on the left pane and then click Restart Now button under "Advanced startup" on the right pane. Click this button and your PC will restart immediately.

How to fix error code 0x80070091 in Windows 10

Step 3: Wait for a while and you can see options on the blue screen. Here you should select Troubleshoot.
Step 4: Select Advanced options under Troubleshoot.
Step 5: In Advanced options, click the option System Restore which uses a restore point recorded on your PC to restore Windows.
Step 6: Select an Account for which you want to restore system, type password and click Next.
Step 7: You'll be asked to select a system restore point. Select the one you want to restore and follow the on-screen instructions to complete the restore process.

Solution 3: Run chkdsk to repair disk errors

Disclaimer: Chkdsk process can check bad sectors for the disk. If any bad sectors are found, disk check process will try to repair them. Bad sector repairing may lead to the loss if data stored on that area. Hence you should take a backup of the data in advance.
Step 1: Launch elevated Command Prompt by right-clicking Start button and selecting Command Prompt (Admin). Click Yes if you get a message given by User Account Control.
Step 2: Type command chkdsk /f /r C: and press Enter key. C: is the drive letter of the partition which contains the WindowsApps folder. If the folder in on a different volume, such as D, you should replace C with D, like chkdsk /f /r D:
Step 3: Type Y and press Enter key if you are asked to provide permission to rest actions.
Step 4: Wait until the checking and repairing process finishes.

Solution 4: Check bad sectors for hard drive

We can use free bad sector software to perform a full bad sector scanning for the hard drive. Eassos PartitionGuru Free is free partition management and data recovery software, providing bad sector checking and repairing function. Please be noted that once any bad sectors are found, you should back up files as soon as possible. Do not try repairing bad sectors without a full backup.
Step 1: Install and launch Eassos PartitionGuru Free from your computer and you can see the main interface showing all disks connected to the PC.
Step 2: Select the hard drive you want to check bad sectors and click menu "Disk" to select "Verify or Repair Bad Sectors" option.
Step 3: The "Bad track verification" window pops up, and you should click "Start Verify" button to start the scanning.
Step 4: The bad sector checking process may take long time to complete if the hard drive being scanning has large capacity. Bad sectors will be marked by red blocks tagged as Damaged.
Step 5: Once the scanning completes, Eassos PartitionGuru Free reports how many bad sectors it finds out.
Step 6: If you've backed up files on the hard drive, you can click "Repair" button to get bad sectors repaired.

Case 2: Error 0x80070091. The directory is not empty

Solution 1: Delete the "windows.old" folder

Step 1: Right click the Start menu to select Run. Then type C:\windows\SYSTEM32\cleanmgr.exe in Run box and click OK.
Step 2: Windows will calculate how much space you can free on drive C: and the process may take a while to complete.
Step 3: Select Previous Windows installation(s) under "Files to delete" and click OK.
Step 4: Click Delete Files when Disk Cleanup asks whether you want to permanently delete these files.

Solution 2: Change ownership for the folder or file

If you have logged on your computer as the administrator and still cannot delete the file or folder, you may need to try taking ownership of the file or folder. Follow these steps.

Step 1: Open File Explorer by double-clicking This PC icon from desktop.
Step 2: Locate the parent directory that stores the files you cannot delete. Right-click on the folder or partition and select Properties.
Step 3: Select Security tab and click the Advanced button for special permissions and advanced settings.
Step 4: Click Owner tab and click Edit.
Step 5: Click the new owner in the Change owner to box in order to change the owner to the selected use.
Step 6: Select "Replace owner on subcontainers and objects" and click OK button. This option changes the owner of all sub-containers and objects within the tree.

Solution 3: Delete system junk files safely

Step 1: Open Disk Cleanup. Click Start menu to look for Windows Administrative Tools and you can see Disk Cleanup.
Step 2: Click Disk Cleanup and a box will appear to analyze files and folders that you can delete safely.
Step 3: When the analyzing is done, you'll be presented with a window where you can select files and folder to delete.
Step 4: Select all dialogue boxes occupied by unnecessary files such as Temporary Internet Files, Temporary files, Old Windows folder, etc. Click OK button to delete selected files.
Step 5: Try again to delete the file or folder that reports error 0x80070091 and check if the error is removed.

Solution 4: Update Windows drivers

Many Windows 10 drivers such as printers, videos cards and network adapters are downloaded and installed during system update. Though it is likely that drivers on your computer are up to date, if you have trouble with a device, you can try updating it manually. Here's the guide you can follow:
Step 1: Open Device Manager. Right-click This PC and select Manage, and the Computer Management pops up. On the left pane you can find and click Device Manager.
Step 2: Expand the categories to locate the device you want to update driver, then right-click on it to select Update Driver. To update hard disk driver, expand Disk drivers and right-click the disk in question.
Step 3: Select "Search automatically for updated driver software" and Windows will search for your computer and the Internet for the latest driver software for the device if this feature is not disabled in device installation.
Step 4: If Windows cannot find a newer driver, you can go to the device manufacture's website to look for solutions.
Step 5: When the driver is updated to the latest, you can restart computer and see if the error code 0x80070091 is solved.

Solution 5: Force delete files or folders using free partition manager

Step 1: Launch Eassos PartitionGuru from your PC and then look for the files or folders you want to delete.
Step 2: Select and right-click files to be deleted and choose "Delete Files Directly" from the context menu.
Note: there is a similar option named "Delete Files Permanently" which is used to delete data permanently. Files can never be recovered if you delete them permanently.
Step 3: Click Delete button to delete selected files. Please make sure deleted files does not include vital system files, otherwise Windows might be corrupted.
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