At the beginning of every .pz2 file, if you open it up in a text editor, you'll see this: { version { number 4.01 } But if it was saved with P5, it will say "number 5.1" or similar. You need to just change it to 4.01 to avoid error messages popping up in P4 or PPP.

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"you are terrifying
and strange and beautiful
something not everyone knows how to love." - Warsan Shire