Stupid unreadable disc error, over and over and over and over

Does anyone keep getting and unreadable disc error anytime they try to play. The first two weeks I had the game it worked great and then all of a sudden my 360 can't read it. The game gets through the credits and to the safe house save point. As soon as I start to move Nico around I get the damn unreadable disc error. I go back to my main menu and there it is, GTA4 completely readable in my tray.
I try to start again and I get the same error.
Someone please help me. The store won't take it back cause it is defective and rockstar should replace it. I waited a year for this game, stand in line, pay 60 bucks and now I am screwed.