Same issue here. The preview render (shift+z) shows it working properly without the fog in the background but trying to render it at all causes it to show a pitch black screen
In preview:
http://i.imgur.com/QUJ1v5b.jpg
when i render it:
http://i.imgur.com/G4Q4IEX.png
The compositing menu:
http://i.imgur.com/aQgMbBP.png