I know only enough about this subject to be dangerous, but whenever I have a model (usually an imported 3ds or obj one) and the surface renders shadowed when it should have rendered as if the light is shining on it instead (because it is), I reverse the normals for the offending group element and it renders OK (usually, but not always).

Intel Core I7 3090K 4.5 GhZ (overclocked) 12-meg cache CPU, 32 Gig DDR3 memory, GeoForce GTX680 2gig 256 Bit PCI Express 3.0 graphic card, 3 Western Difgital 7200 rpm 1 Tb SATA Hard Drives