If disabling the firewall doesn't let you connect, I don't think there is anything else you can do. What I'm saying is that I believe CA/Activision put some tight restrictions on the connection to minimize drops. It seems like they bent over backwards to minimize drops even to the extent of allowing battles to go out of sync. In this game, it isn't enough to maintian a good connection to your friend across the street. You also have to maintain a good connection to the GameSpy server throughout the battle. They didn't have to do it that way, but that's how they did it.

Now what makes it impossible to uncover the cause of the failed to connect is the lousy uninformative error message and the catch 22 on support which is that CA doesn't provide support and Activision Customer Support simply says it's not their responsibility to fix coding errors in the client software even if they are related to the software not working properly with GameSpy. The client software happens to be the game that they published. Activision regularly updates the GameSpy server software, and it's up to the client to maintain compatibility. So they pass the buck to CA who doesn't have to provide any support. You can't get anyware on the problem, and posts about the failed to connect problem in the unofficial support forums have gotten exactly zero response from anyone. There is no way to get any info about it.