Win 9X login problems

I've just updated my servers to Windows 2000, but have a large number of Windows 98 SE workstations in my school's computer labs. These have a problem when a user's password expires. Example of what happens: I create 3 new users with a default password which they must change a first logon. The first to change works fine, the get the "your password has expired, you must specify a new one to logon" message, and are able to chage the password and logon. But when the next 2 logon to the same workstation, they simply get a Microsoft Networking message saying "Your password has expired." The machines won't let them logon. If the machine does a restart, then the next user works fine, but needs to be restarted again for the next. This isn't practical in a school's computer lab.
Has anyone seen this before or do you know a way around this?
All help appreciated.
Kent