I don't think I have seen this at P6, but that may be because I use the Firefly renderer (not implying that it's necessarily better, merely that it is not the same). When I first installed P6, it was reluctant to render anything at all, but a graphics driver upgrade finally appeared which fixed the problems. Since Windows didn't locate any new driver at the time I installed P6, that may be worth checking again, but my early attempts at P6 renders usually didn't get anywhere close to the actual rendering stage, so I suspect that the trouble in the case of your image may be a memory problem.
I generally resort to the Windows Task Manager in those cases. The Poser process (Poser.exe) will have nearly all the CPU (97%+) and a very big figure in the "Mem Usage" column. Even when Poser is working properly, it will take ninety-odd per cent of the CPU during rendering and a large amount of whatever memory is available. When it stalls, it keeps all of the CPU, but the "Mem usage" number freezes. If "Mem Usage" stops updating, then, in my experience, the render has hit the buffers and the only thing to do is to stop the process, because trying to cancel the rendering is already too late. (For that reason, I try always to save a scene before doing any kind of rendering.) It's worth checking the task manager a number of times, before doing anything drastic, though, because the updates to "Mem Usage" can be quite slow. If it updates, however slowly, it's still doing something. If it doesn't, it isn't.
The solution may be to render elements of the scene individually. In the example above, you might render the figure at the back, along with the ground, then the figure at the left, then the one at the right. If the files are rendered as TIFFs, they can be put together in something like Photoshop. The problems start, though, when figures cast shadows on each other, or interact in other ways, because figures that interact need to be rendered together. That can make things complicated.
I was something of a late comer to Poser, so I have used P5 and P6 much more than P4 (I can test things on P4, if necessary). Have you tried using the Firefly renderer and, if so, what happens? In P5, I often found that a render would seem to be going swimmingly, until it abruptly gave up. I never knew what caused that. The render didn't complete, but Poser continued running. The only solution was to try again, with reduced settings for the render job, which usually worked. That implies that there was some sort of resource shortage, but it wasn't one that caused Poser as a whole to lock up.
Sorry for the essay, but I hope some of this helps.