I've just broken a PZ3 with this error.

It was not even an external run-time, but an FBX freebie import. Well behaved, too !! Single rig, 100% original scale, Yay !!

When I found a dozen-plus more such ports by same author --HiGuys920 at DA-- I gathered them all into their own Windows' sub-folder. Which, of course, broke the hard-set paths in that PZ3...

My bad.