invisible vray lights rendering as black circles

[dpcaltdcah]

I have some spherical vray lights with 'invisible' checked that are rendering as black circles. The seem to appear and disappear depending on the camera angle. (see attached consecutive animation frames)

I should add that this is not happening with all of the lights in the scene, just the ones in this particular room. Anyone know what I should do? Replacing the lights doesn't help.

[stevesideas]

Not sure. I was going to say possible negative values on the scale of the lights...but I guess that isnt it. Could it possibly be you have a texture in them that may cause a problem. Are you using a vray camera..are the lights set to lightportal ?