"and at least trying out a new card rules that out!" Yep. Then I'd try swapping out the memory. The strange thing is that it happens with Poser 4 and 5. Are you using the P4 render mode in 5 or FireFly? Does it always happen in the same sequence? Are you rendering to the main window or a new one? Does it happen if you try rendering a bare bones scene, say with one of the default P4 figures? If it happens only or sooner with larger scenes/render sizes then that might poubt to memory but who knows. Let us know how you get on. You might have to call CL to get any response from them.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken