Error when using db library (set to autoload)

[eluser]Ren83[/eluser]
Here is some more info:
This is the default controller from wich i call to Staff controller -

Code:

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

class Main extends CI_Controller {

    function __construct(){
        parent::__construct();
    }

    function index(){

           $question = new Staff(1);

    }
}

And here is the Staff controller wich call to Staff model the i reminded previous post:

Code:

class Staff extends CI_Controller
{
           private $data;
            public function __construct($serial)
           {
                     parent::__construct();
                     $this->load->model('Staff_m');
                     $this->data = $this->Question_m->get_staff_data($serial);
          }
}