IDL in Poser has always had problems.  For the most part it works for most people as they tend to do stills.  however, as RedPhantom says the issue is with the Irradiance caching.  

30 Second commercial by Richard60 (renderosity.com)

In the above video at about 15 seconds in look at the lower right corner of the image and you will see a black blob appears and disappear.  We edited the video to remove most of the blob by zooming in the area that was good (using our video editing software) and leaving out the bad part.   The blob is caused by the Irradiance cache making guesses as to what the lighting should be.  It uses a random number to determine how much and where to sample. The biggest problem is that each processing thread gets a different random number and sometimes you end up with a blob.  Only two ways to deal with it are 1:) render with a single thread and hope you get a random number that won't produce the blob, or 2:) turn off Irradiance caching this will lead to Poser examining each pixel which will take a very long time.

By changing the camera angle a tiny bit will produce another random number which might work well for what you are doing.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13