It looks like you have a .htaccess or something that is preventing or redirecting the url /helpdesk/scp to the error page for your cms/site. Also make sure that /helpdesk/scp exists.
Did you confirm that the /scp exists like I asked? Are you sure that you aren't missing files or something? The DoesNotExist error makes me wonder if things are missing.
Version of PHP? Webserver?
Try looking at your apache error log or php error log and see if anything is being logged.