Image stencil does not work

Hi all,
I'm building an age in URU with blender 2.46 and gow-pyprp 1.5.0.
I have problems with the stencil functionality.
When I use a blend as stencil it works. But when I use an grey image the stencil work in blender but not in URU.
Is this not yet supported in pyprp or did I make an error?
Here are some screenshots
The render in Blender:

The render in URU:
And the config in Blender for the stencil:

As you see in blender there are pebbles only near the edges. In Uru the pebbles cover all
Does someone have an idea what is going wrong?
Thanks
Alex
I'm building an age in URU with blender 2.46 and gow-pyprp 1.5.0.
I have problems with the stencil functionality.
When I use a blend as stencil it works. But when I use an grey image the stencil work in blender but not in URU.
Is this not yet supported in pyprp or did I make an error?
Here are some screenshots
The render in Blender:

The render in URU:

And the config in Blender for the stencil:

As you see in blender there are pebbles only near the edges. In Uru the pebbles cover all

Does someone have an idea what is going wrong?

Thanks
Alex