Normal Map Problem

Hi all!
I’ve a problem with the Normal Pass generated during render. It has only RED and BLU data and all the faces ortogonal to the camera are simply black. In other even some edge result black.
I can’t obtain an image like this http://wiki.blender.org/index.php/File:Manual-PartIV-SuzanneNormalMap.jpg

Can you help me to fix this?

http://twentyfourbecks.wordpress.com/2009/08/30/153/

Many thanks!