Server error

[eluser]solid9[/eluser]
Basic error,

but I don't find the problem of this codes,

Code:

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

class Researchers extends CI_Controller {
public function __construct()
    {
        parent::__construct();
  
  $this->load->model('researchers');
    }

function index()
{
  
}

    function ahe_page()
    {
  $this->load->view('ahe_page');
}

    function add_researcher()
    {
  $this->load->helper('date');

  $data = array(
   'prod_name' => $this->input->post('prod_name'),
   'phase' => $this->input->post('phase'),
   'description' => $this->input->post('description'),
   'main_url' => $this->input->post('main_url'),
   'donation_url' => $this->input->post('donation_url'),
   'last_update' => '',
   'updated_by' => ''
  );

  //print_r($data);
  
  $this->researchers->add_record($data);
  echo 'okay!';
}

/*
    function show_researchers()
    {
        $data['query'] = $this->researchers->show_record();
        $this->load->view('researchers', $data);
    }
*/

}

/* End of file researchers.php */
/* Location: ./application/controllers/researchers.php */

Thanks advanced if you can see the problem.