I had this problem mysteriously pop up a month ago. I didn't load anything new, didn't install any new programs, and my system was exactly the same the day before as it was when I opened it that day. One day, Poser just woke up cranky and decided it didn't want to play. The only way I found to fix it was to reset my "preferences" back to factory state. After re-opening Poser, I re-arranged everything to my satisfaction, and it worked just fine. I think it's Poser's version of a "bad hair day".