Simple stats collection with CodeIgniter hooks

Hi. After hours of googling I find an idea to track users journey throughout the site and to get some quantitative data on on the usage of the application. For example, I want to know when they get connected, the pages they visited (even the functions they called). This is how I proceed.

1)  in application/config/config.php  I replace this line :

Code:

$config['enable_hooks'] = FALSE;

by this one:

Code:

$config['enable_hooks'] = TRUE;

2) In application/config/hooks.php, I add these lines:

Code:

$hook['post_controller_constructor'] = array(
'class'    => 'Track',
'function' => 'track_user',
'filename' => 'track.php',
'filepath' => 'controllers'

3) I create my table looking like :
CREATE TABLE  `audit` (
 `auditId` int(11) NOT NULL AUTO_INCREMENT,
 `userId` varchar(100) NOT NULL,
 `adresseIp` varchar(100) NOT NULL,
 `referer` varchar(200) DEFAULT NULL,
 `controller` varchar(50) DEFAULT NULL,
 `fonction` varchar(100) DEFAULT NULL,
 `url` varchar(250) DEFAULT NULL,
 `navigator` varchar(100) NOT NULL,
 `dateAction` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
 `domain` varchar(100) DEFAULT NULL,
 `pageCourant` varchar(200) DEFAULT NULL,
 PRIMARY KEY (`auditId`)
)
4) Here is my controller:

PHP Code:

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


class Track extends CI_Controller{
    
    
    public function __construct(){
        parent::__construct();
        //    Chargement des ressources pour tout le contrôleur
        $this->load->model('audit_model', 'AuditManager');
        
    }
    public function track_user(){
       // Start off with the session stuff we know
        $options_echappees_audit = array();
        $options_non_echappees_audit = array();
 
        // getting the user
       $options_echappees_audit['agentId'] = $this->session->userdata('login');
 
     // getting the client IP address (we first asks whether it is behind a proxy)
     if(isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {
          $options_echappees_audit['adresseIp'] = $_SERVER['HTTP_X_FORWARDED_FOR'];
      }
      elseif(isset($_SERVER['HTTP_CLIENT_IP'])) {
           $options_echappees_audit['adresseIp']  = $_SERVER['HTTP_CLIENT_IP'];
      }
      else {
        $options_echappees_audit['adresseIp'] = $_SERVER['REMOTE_ADDR'];
      }
       //getting client's domain
       // $options_echappees_audit['domaine'] = gethostbyaddr($options_echappees_audit['adresseIp']);

 
      $options_echappees_audit['navigator'] = $_SERVER['HTTP_USER_AGENT'];

     // REFERER
      if (isset($_SERVER['HTTP_REFERER'])) {
          if (eregi($_SERVER['HTTP_HOST'], $_SERVER['HTTP_REFERER'])) {
                $options_echappees_audit['referer'] ='';
           }
           else {
               $options_echappees_audit['referer'] = $_SERVER['HTTP_REFERER'];
           }
      }
      else {
           $options_echappees_audit['referer'] ='';
     }

     // active page 
     if ($_SERVER['QUERY_STRING'] == "") {
         $options_echappees_audit['pageCourant'] = $_SERVER['PHP_SELF'];
      }
      else {
        $options_echappees_audit['pageCourant'] = $_SERVER['PHP_SELF'].'?'.$_SERVER['QUERY_STRING'];
      }
 
      // Next up, we want to know what page we're on, use the router class
      $options_echappees_audit['controller'] = $this->router->class;
      $options_echappees_audit['fonction'] = $this->router->method;

 
     // We don't need it, but we'll log the URI just in case
      $options_echappees_audit['url'] = uri_string();

     // And write it to the database
     $this->AuditManager->create($options_echappees_audit, $options_non_echappees_audit);
   }
 
} 


But I get this error:
Unable to locate the specified class: Session.php


Why? Please help.
Here is the tutorial i follow:http://7degrees.co.uk/blog/simple-stats-...ter-hooks/