Ok, simple stuff here. The call was:
1. SBS2003 with a single NIC (192.168.16.2)
2. Clients on the same network (192.168.16.x)
3. Clients on a different subnet (192.168.15.x)
4. The server cannot ping ONE client on the 16.x network and cannot ping ONE client on the 15.x network.
Ok, back to "IP Routing 101". So, we can safely assume whatever device that is connecting the two networks has the proper routing table because some of the clients from Network A could ping clients on Network B. My first thoughts were we have to have a goofy static route on either the server or on the two clients -or- the subnet mask is wrong on one of the computers. We did a "route print" from the one client on the 16.x network. No static routes for the 15.x network. While performing the same command on the other client the customer proclaimed "success". He turned off the Windows Firewall on the client!
Customer = 1
Petergal = 0
<I did not clarify whether we were getting "destination host unreachable" or "request timed out".>
Sometimes it's the small stuff! Of course we don't want to leave the firewall off. Adding the appropriate exceptions was the final solution.