Proxy tree shadow problem

[markf]

I have an Onyx tree that I have made into a Vray proxy. In it's object properties I have visable to camera unchecked. So it doesn't render, justs casts shadow. I it's Vray properties I have generate GI and receive GI and visable to GI all unchecked. (I have also tried with all 3 of those parameters checked, no difference in result)

 

The tree is casting shadows on a bit of ground and a simple building. When the tree is hidden the render is fine. When the tree is un hidden it casts it shadow ok. The problem is it causes small irregular patches of the ground and building to not render. It's like the geometry is missing in the patches. The "holes" become part of the rendered alpha channel.

 

I hope I'm explaining this ok. Any ideas or experience with this problem?

 

TIA for any suggestions.