I just noticed that if you make any modifications to CTP2 on your computer, everyone else in a MP game with you has to have the same modifications or you get a "Database Out of Sync" error.
This is redicilous! I guess you have to decide which is more important, modifying or multiplaying.
It was that way in CTP1 too. There is a way to create a scenerio using the basic files, and then modify them. That way the primary files that Multiplayer uses won't be modified. Maybe someone else knows more about this.