One of my users can't log in to his Gforge account. he gets "Your account is locked, please contact a site admin" message.
I edited his user and check the "unlock user" checkbox. but nothing happened and after that the unlock user checkbox disappeared from his user profile.
First question - what version of GForge are you running? There was an issue several years ago where the # of bad tries was not cleared out properly. Getting up to date will prevent this issue from happening to other users.
If you have access to the database, you can run this query to clear the bad data:
DELETE FROM setting WHERE preference_name='lockout' AND user_id=[numeric id];
where [numeric id] is, e.g., 101, 2545, etc.