Windows Networking IP Question

I am running a Novell 6 server and I also use Microsoft peer to peer for one printer for 3 people. It is attached to an XP workstation and shared using MS print sharing. It was working fine for about a year then all of it one of the computers could no longer print. The computer that is sharing the printer and the client computer can’t ping each other when on main network. When I isolate the two computers on a single switch then it works. Any ideas what could be causing the IP problem?