I have an application installed with one of my clients that connects between computers on port 17021.

The problem is as follows:
1. the client application on one computer cannot connect through that port to the server computer... it always responds with 10060 error
2. the same computer can see and use shared resources on the server computer...
3. the client application on that same computer can connect to my laptop acting as a server.
3. the client application on my laptop can connect to the server computer...
4. The same thing happens when I use Interbase which communicates on registered port 3050.
5. Both server and client computer run Windows XP SP2
6. Both ports 17021 and 3050 are open on Windows firewall on server computer...
7. Sophos anti-virus is present on both server and client computers
8. All of the problems mentioned above were not present three days ago, and everything was working fine for about two months since I installed the application, and, according to my client, they didn't install anything new to these computers...

I really need help as soon as possible, if someone ever came across such a problem...