The game is a bit older and designed for XP. This is a not-so-uncommon error for Vista and 7 users trying to play the game, and I'm assuming that's why you're getting this error. There are two ways around this:
1. Set compatibility for the game to "Windows XP."
2. If 1 doesn't work, try "Run as administrator".
Some people have reported their save files missing when doing either of these, so make a backup copy of your save files, or start the game from the beginning if the save won't load.