As someone who feels like they have experience with this problem (http://www.avsforum.com/avs-vb/showthread.php?t=818379
), I'd like to offer my advice:
I have the Xbox 360 HD DVD add-on drive, bought one last November when it first came out, and had SEVERAL problems with combo disks. I had problems with 'The Departed', 'Happy Feet', 'The Matrix' (all 3 in the set)... For 'The Departed' in particular, I had returned and exchanged the disc twice (3 different discs) and always got the same result. I tried boiling the disc, rolling a pen on the side to smooth the side together, nothing worked.
Well it ended up being the drive. After fighting and fighting with M$ customer service (because mine was out of warranty...90 day warranty on a $200 'accessory' is madness I say), I finally got them to waive the $60 replacement fee for out-of-warranty repairs and got a new one.
The new drive they shipped me worked magically and I haven't had a problem since.
So - in MY OWN experience, it was the drive that was faulty the whole time. After I got a new one, things seemed fine. I'm not sure if there are multiple manufacturers that made the drives and perhaps some batches of the drives are bad while others are good, but I think the ROOT cause is the drive that for some reason can't handle the Warner combo discs. It might be a combination of certain add-on drives PLUS certain Warner combo discs, but a replacement drive seemed to do the trick for me.
Good luck, hope you get your problem solved.