Hi all,
I came across a major pain in the rear end today with the NAVT Lists Plugin LINK. After I installed it I could not create menus nor edit existing menus (if imported a MySQL backup) in the admin panel.
As the plugin uses Javascript to administer, there was clearly an error somewhere down the line that cause the whol app to fail. I traced it to the wp-root.php. Make sure the path is correct here...
define("WP_ROOTPATH", "/var/www/vhosts/websitename/httpdocs/");
This worked for me.