I have a brand new copy of Kingdoms of Amular and it always gives me the "Unrecognized Disc" error in my Xbox 250GB Slim. I went through the whole disc troubleshooting list, i.e. clean disc, clear cache, remove hard drive....no luck. Every other game I rent or own will work in the same xbox (I've played at least a dozen other games since this problem appeared). When I put the same Kingdoms disc in my son's 4GB Xbox slim, I can play it fine. This is definitely not an ideal way to play a game this large with all the loading involved.
I also had this same problem with Rage Disc 2. At first I thought it might be the disc, so I exchanged it in the store for another copy...same problem. Put it in my kid's xbox and it works. Any ideas?