My brother and I have had this game for a long while and have never had any problems, however just now when I tried to join his game (online multiplayer rather than split-screen local multiplayer) on my screen I showed up on my screen as being in the game session, whereas on his screen I didn't show up as being there. I could still choose my character etc, and when he chose his the game recognised it and started loading up a game, however we then became stuck on a black loading screen with the words 'waiting for players'. After a couple of minutes, he gets put into a single-player game and I get transported back to the main menu where I am presented with an error message "game session has ended".
He's tried playing with another friend, who had no problems joining in, but when I tried to join their game session we had the same problem (black loading screen, I get kicked to the main menu and they both continue into a multiplayer game).
Anyone have any suggestions as to how to fix this?