Instructions
I downloaded the cleaned Darth Vader file from arhimed and checked it in netfabb Studio Professional. The file actually contained 486 triangles with invalid orientation. I fixed this in netfabb Studio Professional with the following commands
1. remove self intersections (under actions in the repair menu)
2. automatic repair (default repair)
3. select shell (select main shell)
4. toggle selection and press delete to remove the other additional shell
5. status update show one shell, no holes and no invalid orientation.
The select shell/toggle selection/delete sequence obviously run some risk of deleting stuff you actually want in the file but in this case I do not think that happened.
This file has been used in several successful builds in the RepRap machine from Bits From Bytes.