Accnt. Locked Out afterSuccessful Login

I have three users who keep getting locked out of their accounts after successfull logins. The computers are all running XP Pro SP1 and they are logging into an NT 4 server.

When I view the event logs I can see that the user logs on successfully but then the acccount is locked out between 3-20 minutes later. I have not found any unknown username or bad password entries in event log.

Has anyone else experieinced this problem and found a solution for it? We never had this problem before we changed the bad password count to 4 attempts from 7 attemps.

I have reimaged one of the computers and the problem is still happening.