This is an identical copy of the His and Her Owls that is quite popular on the thingiverse. However, the STL file supplied for that model does not work with MakerWare due to "inverted normals" on the female owl, meaning MakerWare was interpretting it as "inside-out" and couldn't render it.

I was able to fix the problem in Blender and re-export it properly. I successfully loaded it in MakerWare and printed it without issue on my MBot Cube II.