XBOX 360 ASSESINS CREED UNREADABLE DISK

i JUST BOUGHT Call Of Duty 4 and when i got to one of the lastss missions the loading screen reads Unreadable disk please clean disk with soft cloth and restart system but the cd has no scratches and the xbox 360 is almost new and i cannot continue on with the game cause the xbox isn't reading the next missions, I changed the dissc and everything workout but now i bought Assesins creed i played till memory slot 4 and the same thing happened de loading screen for entering that particular mission reads unreadable disk please clean disk its brand new, could my console be the problem or are the games coming out with this problems? please help