Unable to UPDATE or MODIFY libraries

[OttoKerner]

Did you modify the location of the Plex data folder, away from the default?

If so:

plex server settings are unavailable 2018

Applies only to Windows: if you moved your Plex data folder to the root folder of a different drive letter: Make sure that you write it as e.g. E:\ (including the backslash \ at the end!) under Settings - Server - General - ‘Show Advanced’ - “The path where local application data is stored”