CI total newbie topic

[eluser]keevitaja[/eluser]
controllers/admin.php

Code:

<?php
class Admin extends Controller {
  function index() {
    echo $this->session->userdata['session_id'];
  }
  
  function login() {
    $this->load->library('simple_auth');
    $this->load->view('login');
  }
}

libraries/simple_auth.php

Code:

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

class Simple_auth {
  function __construct() {
    $this->ci =& get_instance();
    $this->ci->load->library('database');
  }
}

http://localhost/site/index.php/admin/login

An Error Was Encountered

Unable to load the requested class: database

what am i doing wrong? other libraries, like email, do not give the error!