This message usually indicates that either
- the plex data folder is not existing in the location where Plex server is expecting it
- the plex data folder contains inaccessible, or “read-only”, or damaged data
I’m assuming that you are aware that the “Plex data” we are talking about here are not the actual media files, right?
Another issue one must be aware of is this:
If you install Windows completely fresh, all user accounts you create afterwards get a new unique identity (even if you use the same user names as before).
This is normally no problem. However, if you copy old data from other Windows installations, you could get into trouble.
Because the old files and folders might still carry their old “owner” and access permissions which only fit the user IDs of the old Windows installation.
If you copy such data into a new installation, you may have to reset the owner and access permissions of each folder, subfolder, and each file therein.
Failing to do so could mean that some or all files are either inaccessible or “read-only” on the new Windows.
Does the registry backup contain a key to redirect the Plex data folder, named LocalAppDataPath?
If so, at which drive letter and folder does it point exactly? It must match the current storage location of the Plex data, above of the folder named Plex Media Server. More details about this can be found here: [HowTo] An extended guide on how to move the Plex data folder on Windows
