PHP错误查看上个月和下个月的日历

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 The link on the referring page seems to be wrong or outdated.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 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);
    }

}