[agentxi]

hmm, that's a tough one without actually seeing the shader in front of me.

My guess would be to troubleshoot some of the following.

When you are raytracing there are limits to how many raytraces that maya will calculate. By default it is 1. I would change this to 3 or 4 for now and see if it will render any differently. Just keep in mind that if you crank it too high, it will freeze your system, as the higher the number for this, the more resources it will eat. (if the raytracing reaches it's limit it will render the rest as black and same with refraction settings)

If it does not, then I would go onto the lights themselves. Turn up the intensity of the lights and see if that makes a difference.

Also remember when rendering with Mental Ray, to go inside the Render Globals, to go into the Common tab, and turn off "Enable Default Light" as this default light messes up your lighting some.