Hi,
i already read threads like Failed to execute XPath query '//services/plexmediaserver'. and know how to fix this.
If you reinstall Plex, you will get the error "Failed to execute XPath query '//services/plexmediaserver' "
The first fix for this problem seemed to be
Bash
chgrp -R plex /var/lib/plexmediaserver
chmod 777 /var/lib/plexmediaserver
dpkg --configure plexmediaserver openmediavault-plexmediaserver
But after a restart of your server, the Plex service doesn't start anymore. The problem is, that the user/group "plex" and the Folder /var/lib/plexmediaserver aren't deleted if you uninstall plex and this leads to problems on a new installation.
So
1. uninstall Plex (OMV Webinterface)
2. delete the user/group plex
3. delete /var/lib/plexmediaserver
4. install plex again (OMV Webinterface)
this should fix the problem.
(sorry for my english)