Windows 2000 Domain Controller “lockouts”

Hello,
Has anyone experienced having constant lockouts in a Windows 2000 environment? What my problem is that users will wait until the system prompts them to change their password and when they do, if they do, many times we have to change the password for them because they have been locked out in the middle of the day, the system locks them out continually at first logon for days. Has this happened to anyone else? We have no “good” way to clear it up, it usually clears itself up after a little bit of time, but ocassionaly not.

Help if you can,
Matt