I recently bought Assassin's Creed II on steam. I have a Mac. Steam said that the game runs on a Mac.

However, I am having some difficulty getting it to boot up. Every attempt says that Ubisoft has an error or the Ubisoft service is unavailable when I try to enter the purchase code. I have tried it in offline mode which gets me to the login screen, and once I've logged in and it asks for the code I have tried both offline and online but still errors.

I am frustrated and feel betrayed, what do I do?