Random Server disconnects

hello, I have a client who installed RAS/RAC v.2 onto a Win. 2003 Server. He push the v.3 installs to his workstations (16 total), everything seemed to be running fine. Now the client experiences random server disconnects, he has MAC computers(no AV installed) and Window PC's(all running Nod32 v.3) that are connected to this server, and when this problem occurs neither systems can connect to the server. If he reboots the server the connections are back. Anybody experienced this problem before, or have any idea what may be causing it?