I didn't experiment with the scene, but as I see you
haven't set any methods, intervals or samples, it might
have to do with them. Perhaps self-shadowing and
strange interval placement cause this, more intervals
(when using method 2) or more samples (using
method 3) might do it...
--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde
de