Do you have a 32-bit or 64-bit machine? If you have a 64-bit machine (with a 64-bit OS), are you running the 64-bit version of Poser Pro 2010? If the answer isn't 64-bits for both, you have run out of the amount of virtual memory that Windows allows addressing in 32-bits. (This is certainly what is happening to you in Poser 7.) A given process can only use 2-BM of memory. In practice, Poser runs out at about 1.8. If you render in a separate process, this would be the FFE process. You might open up task manager and turn to the process tab, and note how much memory FFE is using.

With Power Pro 2010 (64-bit), I've been able to use up to 12-MB while rendering.