Same problem with Win XP.
My application, running on LAN server, works with Winsock protocol.
When client connect to server, all is OK, but after 4/5 minuts, connection is lost.
If I disable Win XP firewall on client, all works correctly!
Client firewall hav a explicit rule for appliceation (EXE) and TCP port called.
Server machine has firewall enabled and no problem is rised....