Nick, you may need to open up some ports in the router's Port Forwarding. These are the ports you need:
* TCP Ports: 80, 443, 5223, and 10070 - 10080
* UDP Ports: 3478, 3479, 3658, 10070, and 50100
If some of these are closed by your router, this would be blocking the data coming in for your gaming connection.