I've been using GameRanger to play online with a few friends recently and I have encountered this issue as well. At least, the game completely stops working for all of us, but the game is still running and the pause menu is still accessible. We have to save our matches constantly to make sure that we don't lose an hour of progress in a match. I'm not sure if this is the same issue you had, but it seems as if the multiplayer for this game is just buggy. We recently switched over to the AoE franchise for our RTS fix, but I really wish some fix existed out there for the crashing (which seems to be exclusive to multiplayer)..