Lotus Domino 7 will run on a number of Server Based OS’s – which Windows XP isn’t. Could I also assume that this is on a PC and not Server hardware?
Windows XP doesn’t really support any redundancy and will only permit a maximum of 10 connections.
Does the System Shutdown or only the Domino Service? If it is the actual System shutting down then you may need to review the hardware for any issues (Server hardware may have additional logs to review).