Which platform are you on? Are there any marks or scratches on the game disc? When did you first see this error? Where are you in-game when this message appears?
I'm laughing like crazy because of three things you just asked.
1) Are there any marks or scratches on the disk?
Unless something major has changed from PS2 disks, scratches don't cause errors when the game has already "loaded" OR Data loss.
2. When did you first see this error?
when he/her tried to play zombies... duh.
3) Where are you in-game when this message appears?
well let's see here the error is "sound bank failed to load zmb_rt_load.all.you have a built problem". what could zmb stand for? OH I KNOW! Zombie!
*slaps Bkfstwidow* You wonder why i hate Activision Support.
to the OP...
Try deleting all cache and game files and reinstall. Yeah its a pain i know and you shouldn't have to in the first place, but its better than buying a new disk. if on steam then just redownload the game itself.
You mentioned theres "Hardly any scratches or marks" and that kind of indicates that there is at least something on the disc. Please try clearing the System Cache. Here are the instructions:
The error "Sound bank failed to load" could mean the install is corrupt. If that is the case, please try deleting the map packs and re-download. Here are the instructions for re-downloading DLC:
Please let us know how these steps turn out for you.