Ok, so you probably get questions about the hotseat all the time and this might not be the perfect forum to post this in, but I really need help.

I'm trying to play multiplayer campaign with my brother. We're hooked up via LAN. My brother and I get as far as to set up the game and connect to each other. Once I click "start game" my computer will take a few seconds like it's loading the game, then tell me "Medieval II suffered a fatal error and will now exit". What does that mean? We both have the mod that we were trying to play on. We tried playing the Britannia campaign, the custom campaign mod 2, and the retrofit mod- grand campaign. Any ideas?