I'm afraid you can't really compare Blender and Poser... Blender's memory management is much more efficient than Poser's, and Poser has always had issues with handling the way it uses memory.

Unfortunately, there's no way to just point to one thing and say, "That's the problem". You'll have to try some different experiments to see if it can be narrowed down.

Aside from the previous suggestions, you might try removing things from your scene. Make a copy of the file, of course, then start deleting things. Background & texture maps chew up memory, so try them. Try reducing your render settings to a lower value, or try a different renderer instead of FireFly.

If you do these things, and your render gets farther, then we've probably identified a memory management problem. If it stops at the same place, I'd be more likely to go with a morph going out of control, as suggested above.

After you try those things, or if you want more ideas about things we can try, please let us know what you find.