password change problems on win98 client

I have a win 2003 server with AD. I am having problems with password changes on my win98 clients. The user get’s prompted to change the password (as normal) and the user can change their password successfuly. Once the change has been accepted by the server the client is then sent back to the logon screen but cannot logon. In fact NOBODY can logon to the machine unless it has been rebooted. It seems as if the workstation has been denied access to the server after the password change. I had sorted these problems out (various fixes from MS) until I installed SP1 for 2003 server. Can anybody shed some light onto this ? According to MS this problem does not exist. Have setup WINS, SMB signing, disabled encrypt secure channel data (always) on server. Installed DSCLIENT et al on the workstaions.