Hi, if it works with a default VRayMtl, probably there is some problem with the material.
But RailClone doesn't modify the materials in any way. I don't know what would cause that.
I would suggest you convert RC to a standard object (using RailClone Tools or collapsing to mesh), just to check if that fixes the problem.
And of course, to wait the reply from ChaosGroup.
Thanks,