Plutonium

yesterday we played BO2 zombie mode with a friend and everything was ok. Today we are doing the same machinations (hamacha-plutonium-to the host via the IP console), BUT a friend can't come to me, the inscription "Joining game session" turns for a couple of seconds and throws it into the main menu.
We tried reinstalling the game, plutonium, connected via radmin. but nothing helped
what could it be?