This is a known problem with Win98 on an NT network. When the communication session times out (a normal operation) the Win98 client doesn't clear its end of the session, so it can't start a new session when the user tries to print. The communication session is "hung" and can't restart until you reboot. Microsoft produced a patch that is supposed to cure this problem, as well as Win98 clients dropping mapped drives. We found that the cure was worse than the disease, though, because the patch used a lot of conventional memory and we were running a big DOS application.
I don't know if the patch would help you or what its availability is now.