I have a RollerCoaster Tycoon 3 expansion pack, but when I install it, it doesn't launch. When I try to launch the expanded game, an error message pops up saying "wrong disc inserted. Insert the RCT3 disc" or something like that. I try both the original game disc, and the expansion pack disc, but it still says the same thing. Why is this happening? What patch is there to fix it? I am using Windows XP Professional SP3, and the original game works just fine.