Socket Error - 10061

Can anyone help me out here. When I connect an application from a Windows 7 system, port 1500, to an XP system, things work fine.
When I attempt to connect the same application from the same Windows 7 system, to another Windows 7 system, I get a socket error, connection refused. Both W7 systems are in the same network(Home), both systems have their firewalls disabled, and neither have any virus checking software installed. Both systems have their c drive shared and can be seen by each other.
Any ideas how to correct this silly issue?
Thanks

It's a proprietary application that retrieves data from a system running FSX. It is connecting on port 1500, which is open and listening.
(e.g. Win7Sys1 application retrieves data from Win7Sys2 which is running FSX. Win7Sys1 connects to Win7Sys2 thru port 1500, which is open and listening on Win7Sys2)
This works fine where Win7Sys1 connects to WinXPSys2 or VistaSys2. However Win7Sys1 to Win7Sys2 get a connection refusal - socket error.