invite error "Unable to Join Session" HELP

hello everybody, how are you? I installed on my PC and my friend Black ops 2 with the redacted along with the tunngle when we will play together being one inviting the other of the error "Unable to Join Session" being that I can play with random people and he also ... we tested together in a room of a random and we managed to stay in the same play until finished, but we wanted to play together with our own latency of our country and not others ... could help us ?? (and another thing, when the match ends the game gets black screen and crash) " COD : BO2 ZOMBIES