This issue is usually seen as a result of an error while downloading the content. If you have purchased the Rezurrection add on pack for the game, and the Moon map did not download, please do the following:
- Go to the Playstation 3 system menu (XMB)
- Select "Sony Entertainment Network"
- Select "Account Management"
- Select "Transaction Management"
- Select "Download List".
You should see Classic Zombies, Zombies Moon, Theme, and Soundtrack. Select "Zombies Moon" to download the Moon map.