Hmmm, not always the hair prop--- I had massive lock ups with the bone hair and thought that was it-- nope it was the Gargoyle dog. H! Have you ever been able to render 4096x5700 in Firefly?? I never have. I start having probs at 2500 by 2500. And at 4 figures-- count complex hair as a figure, also complex set. Like I say, sometimes it's fine, but otherwise--it's random city!!! Did you boot out and completely reboot your machine?? Did that help or change things at all? Try--I know you are not gonna want to hear this--1200 by whatever and see if it will render. I got the Bone hair one to come across at 1260 by something or other-- not optimum but better than display window. Otherwise, if you really need a dynamic hair piece, use Rdna's. They have always rendered for me-- so far. Emily