I'll be dipped. It does load into P5. Without the figure's morphs, of course. (Can't try in PP, because it uses multiple runtimes and dynamic hair and cloth.)

And after loading into P5, it works in P6. Even though I didn't save the file from P5. (And I have proof that the file was indeed screwed up: the "save to new filename" I did yesterday is still screwed up.)

I wonder if it's the hair and cloth sims that are the problem? Though I didn't save a new pz3 from P5, I played the animation, to see if it worked, and P5 seems to have written new hair and cloth sims to my hard drive.