Was your Poser 5 an upgrade from your Pro-Pack, and then your Poser 6 an upgrade from your Poser 5? Are you then running Poser 6 and then trying to start Pro-Pack? If you are, that's why you get the brief flash of a Pro-Pack screen. They would all be technically licensed to the one serial number, so it is seen by Poser as an attempt to run more than one copy at once and so it terminates the loading of the second program. Just another thought, anyway.