To join to game:
1. The person who created the game must have unblocked posrts 6112 UDP and TCP on his firewall or/and on his router
2. The person joining the game or creating the game cannot be "lagged", sometimes when we are on the chat channel, our character may get lagged. If that happens, exit battle.net and reconnet again.
3. You can't join the game that is already "lagged", for example it can happen that you join a game, then exit it and want to join again to the same game but you can't and a "latency" message will appear