Caustics not working

I have read the RealFX caustics tutorial but I am having trouble.
[img=http://img222.imageshack.us/img222/8065/caustic1pp5.th.jpg]
I don’t know what I am doing wrong. I have set the materials, lights, render settings as the tutorial says(as far as I can tell:D )

Does anyone know why it isn’t working?
EDIT: here is the .blend file
http://files.filefront.com//;7437494;;/