If you try to render a 40 x 40cm pic with standard 300 DPI, your image will become 4724 x 4724 Pixel. That's a lot for non-trivial renders.

Solution may be:

1. Use raytraced lights only. Shadowmaps are stored in memory, raytraced light is computed at runtime (Poser)
2. Change the size of virtual memory (Windows)
3. Add some internal memory (Hardware)
4. Add more internal memory (a joke)

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