I get those occasionally when I use Indirect Lighting. I noticed a few things about them.

• If you save the render as a TIF or a PNG, the alpha layer will contain a hole at those black spots.
• Uncheck the Reflection_Lite_Mult on all materials that does not need them. My best guess is that the lighting is being multiplied too much.
• If possable, do not use the velvet material node with Indirect Lighting. I heard from bagginsbill that the velvet material node has some issue.
• I also noticed that they occur less frequently in Poser Pro 2010 32 bit compared to Poser Pro 2010 64 bit.
• They will change with a different camera position. In a few instances, they will change when you render the image again.
• Most annoying, it occurs in Poser Pro 2012.

I hope my observations will help. I have deleted many renders with this problem.