Mmh ... Could it be, that the ASE loader doesn't support Sub-Materials?
After reading this conversationhttp://188.8.131.52/forums/index.php?topic=5651.0
Materials are 3DS MAX specific. While the loader might be able to support colours (one component of a "Material") - it doesn't.
The answer? use textures.
I thought it was the case.
But after following the code in a debugger, it throws the error on one of the sub materials. It let the others passed. Since it's a graphic artist that creates the model for me, I really have no knowledge of the matter. And he doesn't understand why it's not working.