You could also try deleting any lightFog in the scene as well as any
particle simulations as a test(lightFog currenty has problems with paint
I had a rather subtle problem once with animated self shadowing trees
and flickering. It turned out to be more a problem with a lack both of global illumination and motion blurred shadows… in real life the multiple scattering from leaf to leaf softens the cast shadows as does the effect of motion blur on the shadows. Without this the rapidly shimmering leaves can make it look as if the light is fluttering. I converted paint effects to poly and had the same problem. If you have disable the animation on the trees and still have flicker then it is not this problem.
However I’ve seen another shadow related problem where the tubes suddenly glow at
random frames. It was hard to reproduce and may have been fixed in a past release, so it would be useful to know if you are encountering this problem.
If nothing works you could try converting paint effects to poly( if you can handle the poly count… the pfx->mesh quality window can help get the poly level down ).