I actually figured this out. When you click on CAMPAIGN from the main menu, you have to click CONTINUE, not LOAD SAVED GAME if you load the saved game, it turns the game into a single-play mission instead of the campaign version. It's crap, because I think that if you LOAD a campaign saved game, it should stay in the campaign mode. Anyway, hopefully this helps others.
BTW: just for anyone considering getting this game: DO IT! I can't rave enough about the single-player portion of the game. It's completely gorgeous to the eye and plays nicely on a non-bleeding edge systems. Interface is good (takes some time to get used to, but once you do, it's ON!) and the AI is definately a little lacking... (when is that NOT the case???), but completely playable. The bots do flank and go completely around your area to get you from the back, so it's got some edge to it. I say give it a shot and you won't be disappointed.