non-object and userdata

[eluser]Kemik[/eluser]
Hello,

I'm building a login page for my app and have encountered a problem. I'm not sure why but I get Fatal error: Call to a member function on a non-object in /home/sh/public_html/project/system/application/libraries/auth.php on line 60 when the page attempts to load.

Here's the code (line below comment is 60)

Code:

function logged_in() {
        // Checks if user's session has a user_id in it
        if ($this->session->userdata('user_id') != FALSE) {
            return TRUE;
        } else {
            return FALSE;
        }
    }

Edit: Forgot to mention, session library is autoloaded.