It took me a little bit of work to get that working as well, since I also have my iTunes XML on a networked drive. I’m currently using the full path to the .xml file in the iTunes library XML path field (e.g. /shares/Music/iTunes/iTunes Library.xml) and that is working for me. I also had to change the permissions on the file/folder, since I believe Plex is running as an unprivileged user.
In some other posts I’ve seen, it sounds like you may need iTunes installed on the machine Plex is running on as well for it to be able to appropriately interact with the XML file and library. Here is another forum topic that may be useful:
