Complexity may not be the right word.  Basically, it's a high memory load, which many people hit with they try to create "complex" scenes with lots of scene elements.  But you can burden even powerful computers with a few figures which have high poly counts and high rez textures.  And again, since Poser apparently does a poor job of managing memory use, it seems one can run out after a certain number of renders.  And of course, it depends on your hardware too (e.g., how much RAM you have, swap file size, etc).  That looks like a high poly figure so I can easily imagine your scene hitting the memory limits after rendering for awhile.  Like I said, you can just exit Poser and reload the scene and it should work again.