Windows 98SE User lockeout problem

We have a problem with one user’s account that gets locked out sometimes for no reason. The user’s OS is windows 98SE. We are running Windows NT servers and windows 2000 servers. No other windows 98SE user is having that problem. The lockout happenssometimes when the user tries to open his shared folder on the File server (windows 2000) he gets access denied.Lockout events will occur on the File server but not on the PDC(Windows NT). We tried everything from changing the username, replacing network card, to replacing the ethernet connection. Please Help