Bootrec /fixboot access is denied error generally occurs when Windows fails to get access to EFI system partition. It can also be caused by a corrupted boot configuration data. The nature of this error usually occurs after unsuccessful updates, modification of disk partition or cloning. Sometimes it can also occur after running the Startup repair. For Windows 10 and Windows 11 computers using UEFI, the error can be fixed successfully by assigning drive letter to EFI partition, rebuilding boot files, or repairing the system drive.