I created a simple model theater with a few hanging positions and about 12 fixtures, and focus points. My goal is to practice with modeling and rendering within a model. The lights are turning on fine except as I turn them all on some turn themselves off. The light emitted turns off even though the instrument is turned on in the visualization pallet. If I go to the visualization pallet and turn some other instruments off then the ones that were off turn back on. I've checked everything that I can think of. Any thoughts on what causes this?