Call of Duty 4: Modern Warfare

What happens when you try to play the level?

I would assume your disc is scratched ever so slightly, even if it doesn't appear to be. Try to obtain another disc and try it out. If it loads properly, install it to your HDD. From then on, data will be read from the HDD and not the disc in the tray. The disc in the tray only needs to be readable for security purposes.

To ThePanzerWerfer i cant even start playing the level it will start briefing and do th that pop up thing

This happens to me once. My genius brother scratched my disc to hell by flipping the console while I was playing it. Like knight said, obtain another disc if at all possible. Barring that, you may want to look into methods of repairing the disc, I've heard vasaline can do the trick sometimes.

Your disc is almost certainly scratched or marked in some way. This happened to my copy of World at War, certain levels just wouldn't play. Before getting a new disc though, you could try running the disc under some water, and then wiping it off very carefully and slowly with a towel. Sometimes the disc can get smudged or have dirt on it, and cleaning it could fix your problem.