Something odd happened to me in Bryce. I had an object with several lights attached. The all had volumetric quality. It was working for a while, then it stopped. I've tested a light by itself and it's fine. I've tried resetting the lights, but still nothing. Anyone else have this problem?

I kinda had the same problem , it turned out if there was no ambient light of any kind regardless of how bright the render turned out they wouldn't appear. What I had to do was create a light source away from the camera and then all my volumetric lighting worked.

I figured out what it was. I had several cone shaped lights going with volumetric lighting. I introduced a sphere light w/o volumetric lighting. Doing this caused all my lights to be none volumetric. I don't know if this is a bug or not.