password need to be continually reset

Windows NT 4.0 Server with a domain
Many of the user complain that they cannot access the server resources with their password. No one is allowed to change their passwords but me. The solution each time is to go into the user managaer and simply retype (reset)in their password and click ok. The users can then immediately access the resources. Then in about 2-3 weeks the same thing happens again. A simple reset fixes it. The users do not all claim this problem a the same time and it affects only some computers and not all systems on the network.?