Zombie online mode help :(

When I go into online zombies, look for a map, get into a party, the timer counts down to 0, then it's stuck there and eventually it either says "game session isnt available" or "party has"... something and it goes out of zombies.
So far I can online play solo or private match.

Also: I can't see any lobby chat text.

is your ping good or are you verry laggy?