It happened to me when I downloaded the battle-droid model.
The slow way to do this is to remove every extra skin/level/saber out of your base folder. With no skins or levels in your base folder, it should work fine. Then you can add them back a few at a time to determine the bad material.
Revan: Sometimes I feel like you don't know me at all. (Lightsaber ignites) (Slices) And now, you never will. HAHAHAHAHA!
"Austin..... I am your father."
"No, not really. I can't back that up."