Has there been a solution to this? This seems to happen to me very randomly -- I am able to play some games, and others I can't.
I am behind a personal router, but I tested by plugging my desktop straight into the wall. Didn't solve the issue.
And if my school was blocking the ports, then I would not be able to connect at all. Again, it's just random games that I'm not able to connect to. IF I get in the game, I don't get disconnected from it either. So I think this is a problem with one of the later patches, and shouldn't be dismissed as simply saying 'forward your ports properly'. The issue is with the game that was created itself -- not the connection. It either allows me to join or it doesn't. The next one after it will allow me to join.