User account becoming locked out

We are running three Windows 2000 Servers with active directory. We have about 50 users on it in varing groups. We have been running Windows 2000 for about two months and lately our user accounts keep getting locked out. We have user profiles andlogin scripts that are bing executed at login and seem to be working. There is not any record in the event logs that show that a user is unseccesfully trying to login. Has anyone had this problem or does anyone know of a fix?