Cycles Bake - No Active Uv layer found in the object plane

Hello , I’m triing to bake to a plane surmounted by a cube in blender 2.71.
The program sends a message “no active uv layer found in the object plane” after the uv unwrapping done with the uv/image editor open.
Can Anyone help me? :spin:

I see no blend file !

http://www.pasteall.org/blend/31505

This is a file with a suzanne and a cube around it.
The suzanne bakes correctly, but the cube around don’t have any shadow of the suzanne.
How can I fix it?