My guess is the meta for that admin somehow is corrupt. The only way to fix it is by removing it directly from the database. Use phpMyAdmin or similar tool and delete the only the
meta_key in the
usermeta table for the user id having the trouble.
Hope that helps!
ps. ve very careful of what you delete, there are no backsies … so I highly suggest making a db backup first that way you can revert if things go bad.