Help! "changes could not be saved" when adding a movie library

Plex Media Server
1

Server Version#:1.25.9.5673-bf5697c5d

I have had Plex running on a Mac mini for several years with no problems.
After a recent apple security update, the external drives no longer would mount. To remedy this I installed an older version of the OS.
The external drives now mount, but Plex shows “changes could not be saved” when attempting to repopulate the previous libraries (I did a clean installation of PLEX server after the OS install)

Any suggestions would be greatly appreciated!

2

When you clean installed, did you follow these instructions?