[Plugin: Help Desk] instal failed. Site crashed

just upgraded to latest WP version. tried to instal this plugin but site crashed –

Warning: include_once(/wp-content/mu-plugins/help-desk/functions.php) [function.include-once]: failed to open stream: No such file or directory in /wp-content/plugins/help-desk/help-desk.php on line 33

Warning: include_once() [function.include]: Failed opening ‘/wp-content/mu-plugins/help-desk/functions.php’ for inclusion (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /wp-content/plugins/help-desk/help-desk.php on line 33

Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /home/dwbc2008/the-icoach.com/wp-content/plugins/help-desk/help-desk.php:33) in /home/dwbc2008/the-icoach.com/wp-content/plugins/wordpress-automatic-upgrade/wordpress-automatic-upgrade.php on line 121

Fatal error: Call to undefined function is_site_admin() in /home/dwbc2008/the-icoach.com/wp-content/plugins/help-desk/help-desk.php on line 67