We are from germany, but we bought the game. The german version is cutted so we have to use a patch to get it uncut so we can play Zombies. Could this cause the Problem?

When me and my brother try to play W@W Coop we get the error: "game session is no longer available"
I tried everythings, but i still not workling. We have good Connection, and there are even Random People joining my host.
Someone know how to fix?