Session requires login after login

I have a website that has a  login requirement to access functions on a certain controller. The login portion works fine and I can access one of the functions in the controller. But if I try to access any other function the log in screen pops up and requires me to log in again, however I can never get to the page I want it will just ask me to log in again. Below is a php code. The main controller handles all of the login functionality. The ATIS controller checks to see if the user is logged in. 

ATIS Controller (The secure section)

PHP Code:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Atis extends CI_Controller 
{
        public $status; 
        public $roles;
public function __construct()
    {
        parent::__construct();
    $this->load->model('User_model', 'user_model', TRUE);
    $this->status = $this->config->item('status'); 
    $this->roles = $this->config->item('roles');    
    $this->is_logged_in();
    }

public function index(){   
    $this->load->view("atis/inc/header");
    $this->load->view("atis/dashboard");
    $this->load->view("atis/inc/footer");
    }
public function is_logged_in() 
{ 
$is_logged_in = $this->session->userdata('is_logged_in'); 
if(!isset($is_logged_in) || $is_logged_in !=TRUE) 
{ 
redirect('main/login'); // If I take this out I can access the other functions previously asking for me to log in again but takes away the necessity to login to view the other functions. 
exit(); 
} 
} 


Main Controller (Where the login function happens)

PHP Code:

public function login()
        {
            $this->form_validation->set_rules('email', 'Email', 'required|valid_email');    
            $this->form_validation->set_rules('password', 'Password', 'required'); 
            
            if($this->form_validation->run() == FALSE) {
                $this->load->view('inc/site_header');
                $this->load->view("site_nav"); 
                $this->load->view('login');
                $this->load->view('inc/site_footer');
            }else{
                
                $post = $this->input->post();  
                $clean = $this->security->xss_clean($post);
                $userInfo = $this->user_model->checkLogin($clean);
                
                if(!$userInfo)
                {
                    $this->session->set_flashdata('flash_message', 'The login was unsucessful');
                    redirect(site_url().'main/login');
                }
                else
                {
                    foreach($userInfo as $key=>$val)
                    {
                        $this->session->set_userdata($key, $val);
                    }
                    $this->session->set_userdata('is_logged_in', TRUE);
                    redirect(site_url().'atis/');
                }
           } 
        } 


maybe you forgot to load the session library in the controller which the login process happen.

Just a random guy from Internet

The session library is autoloaded