If the error persists after all steps, the underlying issue is likely a failing hard drive (bad sectors in the zone directory) or a Windows User Profile corruption. Test with chkdsk /f and create a new Windows local user account for gaming.
Before trying anything complex, use Steam’s built-in repair tool: Steam Library Right-click on Call of Duty: Black Ops II (Multiplayer or Zombies). Properties Installed Files Verify integrity of game files missing config file default-mp.cfg black ops 2