Login Function Works Locally But Not When Live?

[eluser]JamesTaylor[/eluser]
I am using the following code to check whether a user is logged in, it works as expected when used in the local environment but now i have uploaded the site to a temporary live location it doesn't work?

Whats strange is that i'm sure this work previously when i had uploaded to a temporary live location and the code hasn't been changed since?? That could just be an issue i didn't notice at the time but it would be a pretty big thing to miss!

Code:

class Home extends MY_Controller {

//Makes check for logged in run each time
    function __construct(){
    parent::MY_Controller();    
    
    $this->checklogin();
        
    $this->output->set_header('Last-Modified: ' . gmdate("D, d M Y H:i:s") . ' GMT');
    $this->output->set_header('Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0');
    $this->output->set_header('Pragma: no-cache');
    $this->output->set_header('Expires: Mon, 26 Jul 1997 05:00:00 GMT');    
    }    
    
//Check Session data to see if logged in    
    function checklogin()
    {
    $admin_is_logged_in = $this->session->userdata('admin_is_logged_in');
    
    if(!isset($admin_is_logged_in) || $admin_is_logged_in !=true)
        {
            redirect("Admin/LogIn");
        }
    }

It seems that at present the when view in the live location none of the code function __construct() is actually run as if i place an echo value anywhere within it nothing is returned, yet when i do this locally the echo value is written as the 1st thing on the page??

Can anyone point out my wher emy mistake is here?