I used to render the same scene 30 times, tweaking away at lights and shadows. Then turn the cam 5degrees and lockup. Reboot last successful pz3 and ! lockup. Do it 5 times and lockup! Turn it off in disgust and unplug it from the wall.... Have it work. This was P5. Saving all your props and figs with all their alterations and reimporting them new has been lucky for me. You should be able to do three of these.