If you're using Poser 6 (and you seem to be), periodically minimize Poser while the render is running; from experience, the renderer will fail to release memory after it's done with a bucket, and the process the renderer runs under will gradually bloat up and die.  edit: note this is no longer a big issue in Poser 7, but for me in Poser 6 it was often the only way to get many scenes to render.

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