You can fix Error 0x80070091 in Windows (usually happens when deleting folders like WindowsApps) by restarting your PC, running chkdsk, using Safe Mode to delete the folder, or running sfc /scannow and DISM to repair system files. If it’s a WindowsApps folder issue, take ownership only temporarily, delete it, then restore permissions. Avoid random “permission fixer” tools—they can break system folders.