FATAL ERROR: Fatal error: Call to undefined function wp_register_plugin_realpath

It appears you’re replacing the default plugin.php file but either it’s not up to date or something, haven’t looked into it, but basically makes the persons WP unusable and then you have to get copy of plugin.php from SVN just to get working again

Fatal error: Call to undefined function wp_register_plugin_realpath() in /home/myles/cloud/WS/test/wp-settings.php on line 178

For others who need it here’s 3.9.2:
http://svn.automattic.com/wordpress/tags/3.9.2/wp-includes/plugin.php

https://wordpress.org/plugins/hook-sniffer/