After the latest crash, all my material assignments are corrupted somehow. I've seen two different embodiments of this. The first renders the material completely clear (the part looks like a wireframe). The second simply shows it completely black. The material is 6061 aluminum. Removing the material, saving and re-attaching it seemed to work. But it proved not to be a reliable fix. I also tried "Save As". -Martin 2005sp0.1