Restricted connection to the server program

I have 40 payment terminals which keeps sending transaction back to a server
program being run in Windows Server 2003. One individual is used to transafer
each TCP/IP connection. (i.e. when one transaction is sent, connection is
closed and new transaction is opened for the next transaction). The first
1million transaction sent from the Terminal are fine. But after then, the
connection from the payment terminal is restricted and the Terminal failed to
connect to server.

We suspect that windows server 2003 has an mechanism which restrict the
repetitive connection from the same IP address. The same test being run at
Windows XP doesn't have any problem. If there is really such protection in
2003, is that any way to disable such connection?

Thanks!

Tony Siu Chun Tung