I can't say, that I do have any problems cancelling a render. One click on the button and after a couple of seconds the render is cancelled. No need to shut down Poser. If the render runs out of memory I get an error message suggesting to reduce bucket size, turn of texture filtering or to change another setting I can't remember now. I've tried with a pz3 file I never got rendered in P5... So far P6 wasn't able to finish it, but at least I get the message and can cancel the render to change settings without restarting Poser :)

Yesterday's the past, tomorrow's the future, but today is a gift. That's why it's called the present.