DI-604 port forwarding problem. Very puzzling..?

My friend and I are learning about networking with Java. We wrote a program that has a client application and a server application. We never got it working between the two of us, never with him, and I can only be a client when someone else is the server.
When using two other people though, the code will work. So we have determined the code is not the problem.

I've basically narrowed it down to the routers, and likely a port forwarding issue. He has a DI-704, and I have a 604.

I fumbled around for a while and came to the same conclusion as this tutorial I found on this site: http://www.portforward.com/english/r...04/default.htm The program still will not connect.

I'm confused. And depressed. I am 192.168.0.101 behind the 604, always and forever. I do not for the life of me understand why this isn't working.

Here are the settings I'm using for the Virtual Server:
Enabled: True
Name: Alfx's Game
Private IP: 192.168.0.101
Protocol Type: Both
Private Port: 9876
Public Port: 9876
Schedule: Always

And then I hit apply. And it's checked in the list below.

Any ideas? Help would be greatly appreciated.