无法找到指定的类：codeigniter中的Session.php

Question

   class Test extends CI_Controller 
   {
     public function __construct()
     {
        parent::__construct();
     }

     public function index()
     {
        $data = array();
        $this->load->library('../controllers/front/booking.php');
        $Booking = new Booking;
        $data['menu'] = $Booking->process_handled_response($sata);
    }
 }

    Booking.php 
    class Booking extends CI_Controller 
    {
       public function __construct() 
       { 
         //calls till here
         parent::__construct();
         // aftr this it doesnt
         $this->load->library(array('session'); 
       }
    }

    public function process_handled_response($data)
    {
        echo "111"; exit;
    }
}

Error : Unable to locate the specified class: Session.php Test Controller calls a Booking controller function But it shows the above error.It loads library and can call booking.php till //calls till here after parent::__construct(); it shows error.