PHP在日历库中显示上一个月和下个月时出错

Question

In here it displays the calendar but when ever I click next or previous link it show this error:

Object not found! The requested URL was not found on this server. The link on the referring page seems to be wrong or outdated. Please inform the author of that page about the error. If you think this is a server error, please contact the webmaster. Error 404

Please please please someone help me!!   


 Project name: ci_series
         config.php I set the base url as http://localhost/ci_series/'
         $config['index_page'] = '';

          I used cordelginer framework.My welcome controller is the one    defaultly loading.

         welcome.php

         <?php

          class Welcome extends CI_Controller {


        function index()
        {

            $this -> display( $year=null, $month=null);

        }
        //display function
    function display($year=null, $month=null)
        {
            $conf= array( 
                'start_day'=>'monday',
                'show_next_prev' => true,
                'next_prev_url' => base_url(). 'display'

            );
            $this->load->library('calendar',$conf);
            echo $this->calendar->generate(  $year, $month);
        }

    }