Thanks Ian – I will correct this. I found this example for it: http://wpfirstaid.com/tag/wp_enqueue_scripts/
If you enable the Debug Bar plugin, you can see some other warnings being issued:
WARNING: wp-content/plugins/toppa-plugin-libraries-for-wordpress/ToppaAutoLoaderWp.php:39 – include(/var/www/vhosts/[redacted]/httpdocs/wp/wp-content/plugins/toppa-plugin-libraries-for-wordpress/WP/User/Search.php): failed to open stream: No such file or directory
WARNING: wp-content/plugins/toppa-plugin-libraries-for-wordpress/ToppaAutoLoaderWp.php:39 – include(): Failed opening ‘/var/www/vhosts/[redacted]/httpdocs/wp/wp-content/plugins/toppa-plugin-libraries-for-wordpress/WP/User/Search.php’ for inclusion (include_path=’.:/usr/share/pear:/usr/share/php’)
WARNING: wp-content/plugins/toppa-plugin-libraries-for-wordpress/ToppaAutoLoaderWp.php:39 – include(/var/www/vhosts/[redacted]/httpdocs/wp/wp-content/plugins/simpletest-for-wordpress/WP/User/Search.php): failed to open stream: No such file or directory
WARNING: wp-content/plugins/toppa-plugin-libraries-for-wordpress/ToppaAutoLoaderWp.php:39 – include(): Failed opening ‘/var/www/vhosts/[redacted]/httpdocs/wp/wp-content/plugins/simpletest-for-wordpress/WP/User/Search.php’ for inclusion (include_path=’.:/usr/share/pear:/usr/share/php’)
It complains about files missing from your library plugin, even though it’s installed and activated.