If you are using the Plutonium launcher or custom mods, the game may be looking in the wrong folder.
It sounds like you're dealing with the classic "exe cannot find zone" Call of Duty: Black Ops Exe-cannot-find-zone Black Ops Fix
If none of these work, please specify which map or mode (Campaign, Zombies, Multiplayer) you were trying to launch when the error occurred. If you are using the Plutonium launcher or