Server not available

After three weeks of smooth operation, SOA started giving me this message: Server not available.
The network is peer to peer. The operating system is Windows XP Pro sp3.
I tried repair option but that did not make any difference.
We have a filtering system (Comsift) on the network. It acts as DHCP server. This computer is set to bypass all filtering.
I have not done an uninstall of SOA (doesn’t seem promising).
Help