What happens during an out-of-synch?
When there is an out-of-synch during a game, for example, if a person is somehow disconnected from a game, Civ4 will pause the game and bring up a voting screen. Unlike Civ3, which would normally crash during an OOS, Civ4 allows you to vote on what you should do: save the game, wait for the player, or continue on. Because of this, an error during a multiplayer game is not too devastating – you can simply just wait for the person to reconnect.
