Win98 Kicked off 2003 network

Most of my clients are Win98 PCs, Sometimes these PC cannot connect to the
network, the error is "Access to your domain server is denied or your
password is incorrect" (something like this). If we reboot the PC and logon
with the same info the PC works fine.
This error happens everytime for Win98 Clients which share a printer, if
someone print to that share, they are then unable to print back onto that
share, if you goto the sharing PC and try and logoff/logon you get the error
message above. This has only started happening since we upgraded to 2003
with AD.

Please Help.