Zombies mode often relies on assets found only in the Multiplayer installation. Search your Steam library for .
Are you running the version or a custom client like Plutonium ? black ops 1 error execannotfindzone extra quality
If the folder is in the right place, check the files inside the mod folder. You should see a .ff file. If the folder is empty or contains only images/text files, your download was corrupted or incomplete. Re-download the mod. Zombies mode often relies on assets found only