Most users fix the error by verifying game files in Steam, restoring quarantined DLLs from antivirus, or reinstalling the game into a non-protected folder with correct permissions.
Did this fix your game? Let us know in the comments below. For more Black Ops 2 error fixes (like "Server is not available" or the infamous "UI Errors"), check out our tech support archive. black ops 2 cannot create steam-api.dll