Outlook password expires in 0 days?

I am having a problem with web based email with Exchange Server 5.5 SP3. When users login to their mailboxes via the web, the message, “Your current password is about to expire in 0 days. To change your password, go to the Options page after you login.” When the users go to Options to try and change password, it tells them that the username could not be found.

The user accounts are set to never expire, so what could be the problem?

Thanks for any advice.