you may have reset the administrator permissions on that part of the registry to "full" before being able to delete it/them. To reset the permissions right click on the registry item, select permissions, click on administrator, then give yourself as admin, the permissions you want, you may have to revoke "system" permissions, to prevent "system" or whatever may be running in the bg, from blocking the admin from applying the changes.. To low level edit the registry, try saving it/exporting it, and editing the backup, maybe regedit is able to edit backups? then re-import after editing..