For me, it's a corrupted texture file or something P6 cannot find from a previous version. I would minimize and wait for restore to appear. As soon as you are in, go to display>libraries and change that material to anything in reach (1st click). Then exit matroom. Reenter and choose correct texture. Your call but, I see the pesky stairs.pmd file on your desktop...this binary morph filing can be disabled for simplicity. Or delete all props and figures not in scene and save as new.