It IS generally a memory problem. My Poser 6 tells me the same if I try to render things with large textures (like V3) and accidentally turns Texture filtering on. I don't think the psd thing is an issue but you could try saving them as jpg's (high quality) and see if it helps on the issue...

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.