Dude!, I haven't finished reading your tutorial yet and I already love you.
You just fixed a problem I have with the following explanation:
"There is a feature called “Light shape visible in rendering”. Unless you know what you are doing, you should never use this. Otherwise you will end up with fireflies on your materials. "
I posted this issue on cgarchitect:
I actually gave up and disable the photometric light and rendered another view, but I'll go back and try it again.