php中没有定义站点错误

尽管我已经将PHPMailer_5.2.4文件保存在我的CodeIgniter_2.2.0中，但它显示class.phpmailer.php不在本地磁盘中。我已经确认PHPMailer_5.2.4中有class.phpmailer.php。

代码如下:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
require('PHPMailer_5.2.4/class.phpmailer.php');
class Site extends CI_Controller {
public function __construct(){
        parent::__construct();
        $this->load->model('site_model');
        //$this->load->helper('url');
    }
    public function index(){
        $this->load->view('welcome');
    }
    public function view(){
        $this->load->view('registration');
    }
    public function generate_token ($len){
        // Array of potential characters, shuffled.
        $chars = array(
            'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 
            'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 
            'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'
        );
        shuffle($chars);
        $num_chars = count($chars) - 1;
        $token = '';
        // Create random token at the specified length.
        for ($i = 0; $i < $len; $i++){
            $token .= $chars[mt_rand(0, $num_chars)];
        }
        return $token;
    }
    public function insert(){
        $token=$this->generate_token(7);
        $this->load->site_model->insert($token);
    }
}