Black Ops 2 streamed sounds directly from the hard drive or disc to save memory. But on slower drives (or drives with bad sectors), the game’s audio manager would request the “cmnrootenglish” bank before the file system had fully mounted the storage device. The game engine, impatient and strict, would throw the error and crash rather than wait.
Use the built-in repair tool to replace corrupted or missing sound banks: Steam Library Right-click Call of Duty: Black Ops II Properties > Installed Files (or Local Files). Verify integrity of game files Adjust Windows Sound Settings: black ops 2 sound bank failed to load cmnrootenglish best