Question about the XBOX 360. . .?

Well I just bought a XBOX 360 for Christmas, and I got Call of Duty World at war. The game is fine, and the XBOX 360 reads "This game is unreadable" only on 1 level. All the levels it is fine, but on this one level "Blood and Iron" it doesn't read. Do any of you know of a way I can fix this? My brother didn't get to finish story mode because of this.