Each external parent folder must have a runtime folder within.  you can easily link to those folders as Dr. Geep illustrated.  If you still have P6 installed, navigate to the P6 folder only, do not target it's runtime folder within for linking.  By your OP, am I to assume that you are trying to access pz3's?  If that is the case, the open command under files will suffice. However, you would need to re-establish all links for the scene to load properly.