Hey guys, I'm just getting started in this whole thing, so of course I've gotten the dreaded non-manifold errors. However, Shapeways' online visualizer isn't displaying my model. I'm using Cinema 4D on my Mac to create my models, and wasn't able to find anything in the help about error checking models, so I'm wondering if there is any small stand alone progam to do this on OSX. If there is nothing of the sort I suppose I'll just go ahead and get Blender. Also, does anyone know of a good resource on non-manifold and inverted normals, what causes them, how to fix/avoid them, etc. I've been searching the web and other than what's here, I haven't found anything very comprehensive. I really just want to get a better overall understanding of what's going on. Thanks!