redirect() throwing error

[eluser]VirtualDevel[/eluser]
Hi guys, I get the following error when I call redirect() :

Fatal error: Call to a member function site_url() on a non-object in /var/www/vhosts/[host-name]/httpdocs/system/helpers/url_helper.php on line 45

Here is the code in the controller:

Code:

if ($this->do_upload()) {
   redirect('/admin/stuff/editor', 'refresh');
}

Not sure why I am getting this, any ideas?