In the library manager, click on the folder with the arrow pointing upwards untill you see two folders called "Poser5"(with a red indicator) and "downloads". If you now click on the small triangle pointing downwards, you see at the bottom of the dropdown with Camera, Figures etc an option to add a new runtime folder. Simply point this to your P4 folder. Should work flawlessly.

I have tried prudent planning long enough. From now I'll be mad. (Rumi)