Yes, thank you so much BW! Book 2 is now working on my Mac. Seems that I have to start over as all of my saved games have magically disappeared, but that's OK. I can play Book 2 now!
I realize that I'm a little late to this party, and that BasiliskWrangler is working on the issue, but I also am having the exact same issues with both Book 1 and Book 2. Neither will start since I have upgraded to Lion (other Steam games, such as Civ IV do), and they give error output ...