So far I have found out that it depends on what type of XBOX you have. If you have the original one or the new one then problem might be that you have some sort of external memory device plugged into the console (i.e. USB Drive, Memory Card, etc.) other than the Hard Drive. If you remove any of these, besides the Hard Drive, it might fix it. Other than that, I found that looking through all your memory devices and searching the Modern Warfare 3 section and removing any Corrupt Files (marked with an exclamation point surrounded by a yellow circle) will temporarily put a halt to the Unreadable Disk error.
When troubleshooting console issues, there are 3 variables that could be causing the actual issue. The game disc, the game data, and the console are the 3 variables.
1. Make sure to delete all game data for the game and let it redownload any patches that it requires:
To clear the cache on the Xbox 360 do the following:
Go to the Xbox Dashboard, select the Settings menu, and select System.
Highlight the HD symbol and press Y.
Select "Clear System Cache".
1. Navigate to your System Settings.
2. Select Storage.
3. Select Games.
4. Locate and delete all files associated with Modern Warfare 3.
2. Test your disc on another console. If the disc works fine on another console, the issue is not the disc. If you find that the game does not load on another Xbox 360, Activison customer support can begin to process a warranty disc replacement if the disc is within the 90 day warranty period and there is no damage on the disc. Please keep in mind, your disc is tested and inspected upon delivery. If your disc is received with damage or it is no longer within warranty, there would be a 20 dollar replacement fee for the disc.
3. If the previous steps did not resolve your issue, there may be a problem with the hardware within your console. You may want to contact Microsoft for further support:
Xbox Live Customer Support:
* 9:00 A.M. to 1:00 A.M. Eastern Time
* 6:00 A.M. to 10:00 P.M. Pacific Time
* Toll free: (800) 4MY-XBOX or (800) 469-9269
* Direct dial:(425) 635-7180
* Hearing impaired (TDD device): (866) 740-9269 or (425) 635-7102