Brazil render turns black when light is turned on

I purchased Brazil after the previous conversations on the Forum and have been learning it for the past few weeks. I am really pleased with how the renders of gemstones have been turning out.
I have placed a point light inside the crystal and have got this result. But now when I try to do the same render with the light on, the render turns out completely black and there are no signs of the processing squares.
When I turn the light off the render is excellent and the processing squares bubble around the render as usual, but the render does not have the light flecks on the floor.
I am suffering from instruction blindness and am hoping that someone can point out my simple mistake. Also I would appreciate any other tips as to get a better render quality.

here`s hoping


I’m not able to reproduce this here, so it may be a material or setting causing the issue in your file. Can you send it to to my attention? Or post it here and I’ll take a look.

I sorted it out eventually, Im not sure exactly what the problem was.