Exactly the same problem here, seems to affect a quite a few cars, mine was four years old when it started. Dealer said I didn't have the darkened rear window, I bought the car second hand so assumed a tint had been put on, of course it hasn't, just anything to get rid of me. Car looks a mess, not good for resale. As I understand it the whole roof would need replacing so no wonder BMW doesn't want to admit it's a fault!