Very odd. The same thing happened recently with my step brothers copy of CoD:MW3... The game disc was in PERFECT condition (no scratches or indents in the disc at all) and the game would start up normally, but after maybe 5 minutes of playing it would say that the disc is unreadable and it should be cleaned with a soft cloth, etc. I tried to install the game to the hard drive and it would give me an error about 50~% of the way through. This I the ONLY game I have encountered to do this on my system. I could not figure out a solution to this disc's problem. So my answer was purchasing another used copy from Gamestop and swapping it out with my copy. Very odd, I do not know what the issue was.