Codeigniter lost session when cross controllers - php

Question

I created a Facebook login on my site, then when I get data of a user logged, I created an array session to store the information of users in my controller.
I have problem with this session when I go to another page, my session gets lost, I don't know what happens with this?
I set the session like this: $this->session->set_userdata('fb_user_info', $user_info);
But, my own account login, I do the same way, it works on all pages.
My question is, Why does the session get lost?
Here is my code to set session when get user_info
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class Account extends CI_Controller {
public function __construct()
{
parent::__construct();
//$this->authenticate();
// Facebook constructor code
$CI = & get_instance();
$CI->config->load("facebook",TRUE);
$config = $CI->config->item('facebook');
$this->load->library('facebook', $config);
public function index()
{
$user = $this->facebook->getUser();
if($user) {
try {
$user_info = $this->facebook->api('/me');
// Set session
$this->session->set_userdata('FB_SESSION_INFO', $user_info);
$args = $logout_url;
$data['getLogoutUrl'] = $this->facebook->getLogoutUrl($args);
} catch(FacebookApiException $e) {
echo '<pre>'.htmlspecialchars(print_r($e, true)).'</pre>';
$user = null;
}
} else {
$param = array('scope' => 'email','redirect_uri' => $mycurrent_url);
$data['getURLLogin'] = "Login with facebook";
}
}