I've got a model built in Electric Image Modeler, exported to .obj format, that I'm trying to render in Maya 5.0.1 using Mental Ray, but when I place a light directly over the model, the illumination on the model is reversed as if the light were beneath the model rather than above it. Stranger still, the shadow being CAST by the model correctly appears on the floor beneath the model. If I switch to Maya Software rendering, the illumination is correct. What in the name of all that is sacred is happening here?
Have you tried reversing the normals? Flipped normals often occur when switching between apps. Maya Soft-renderer by default renders both sides of faces(I thought mr did too, whatever..). You could try switching to back or both in the General settings in render globals but its better to make sure you