Sometimes when I try a render with ray tracing turned with the firefly renderer in P6, the skin of the model has dark spots - almost like those on a leopard. What is strange is that turning off the shadows in the lights, but checking "casts shadows' in the firefly box still produces the spots. When I use the non-ray traced shadows (turning off ray tracing in the lights and render menu), the spots disappear... Any explanations? What am I doing wrong? thanks

Check your ray trace bias in the light settings and adjust it up or down and see if that helps.