SR2.1 fixes a lot of bugs, but not the lights or memory usage (although it does improve it). Large scenes with high res textures increase the chances of lockup. I seldom have the problem with a P4 type render, but I usually lock up once a day or more in firefly. One of the best things to do is to get the everything the way you like it, and save then. Try your render and if it locks up, kill Poser, reboot, and try again with fresh memory. If it still doesn't work, start working with the lights. Save before every attempt. I've lost at least a dozen projects because I was in a hurry and didn't save (like an idiot). Has CL said anything more on SR3?