Based on some updating/fixing, I wanted to test updating the XML in Plex. It is failing to import. I got that same error message you reported.
Here's what I did
I closed iTunes. I made a copy of the XML file and put it in a different folder and called it "iTunes Library (COPY).xml. I made the proper edits to the XML file. I saved it as iTunes Library.xml.
Then I followed these steps:
1. I logged out of Plex on the website.
2. I went to the Plex Media Server on the NAS and stopped it.
3. I then uploaded the new updated XML file and replaced/overwrote the existing XML in my Music1 folder on my NAS. I checked on the NAS to make sure it was the newer file (it was) - it had today's date and was only a few minutes old.
4. I restarted Plex Media Server on the NAS and launched Plex.
5. I went into Plex and did this Music > ⋮ > Scan Library Files followed by Playlists > ⋮ > Import from iTunes... with the option to Overwrite existing playlists.
After getting the error, I scanned the files again and tried importing again. I also logged out of Plex and stopped, then restarted Plex Media Server on the NAS once again. I then tried again, scanning the files, then tried importing the playlists. I keep getting the error message and the XML is not updating.
One thing I did not do - which was part of your initial instructions when you got things working - was that I did not disable the itunes plugin or remove the XML path. I kept both of those as they were set.
You had unchecked the itunes plugin and then shut off Plex Media server and restart it I have in my notes. Then you added the XML path. Do you think I should do that as well now, again? That doesn't seem logical, but perhaps we need to sort of reset the table so to speak but I'm nervous about doing that as I don't want to lose my playlists for some unexplained reason if this somehow did something.
Can you tell me if you think I did anything wrong here?
Have you tried another album or two and maybe a couple new playlists? I'd be curious to know if yours was successful. BTW, what I did to test to see if it worked was to edit a couple of playlists that were successfully imported. I then changed the name of an album (which had asterisks in the name of it) to see if that came through.
No adverse changes occurred on the attempts to import the playlists or any other music that I could detect. But before I do more work on updating/fine-tuning Plex, I sure would like to know why the updated XML isn't coming in.
This was another comment related to this that you made.
The XML file in your iTunes library folder will be updated each time you make a change to the library, e.g. edit a playlist, add some metadata, or just play a track which increases the play-count. Plex should detect metadata changes by itself,
but when you want it to update the playlists or you've moved/renamed any files, copy the XML, edit out the unwanted double slashes, save the copy in the volume1/Music1folder as iTunes Library.xml then use Music > ⋮
> Scan Library Files followed by Playlists > ⋮ > Import from iTunes... with the option to Overwrite existing
playlists. The is no point copying the updated file back to C: as Plex isn't going to change it, and you'll want the current version produced by iTunes next time you want to refresh the playlists.
I'D REALLY APPRECIATE IT IF YOU COULD SEE WHAT I'M DOING WRONG AND HOW TO MAKE IT RIGHT.