Yafray rendering problems

I have two problems with rendering with yafray. In my scene I have a glass box (the sort you find in museums enclosing an artifact) with a marble base. The base becomes all splotchy and oddly colored as if the light from te HDRI is horribly refracted even though the glass is completely flat and thin. Any way to fix this?

Secondly, when I try to render one of the layers it always comes up with and error that “object Empty.088” cannot be found and crashes blender, even though there is no such object in the layer or in the whole scene, as far as I can see.

Thanks in advance.