With an attitude like that its no wonder you still have an issue.
Works fine on my AE-5.
They've known about the issue since launch but they have no intention of fixing it, Forza 3 was fine, literally every other game released in the last 15 years is fine, but not Forza 4.
I just won't buy anything from Microsoft's store again until they sort out their refund policy. Not worth it.