Fatal error: Call to a member function insert() on a non-object in ?

[eluser]anna16[/eluser]
by the way this is my site controller codes,

Code:

<?php
class Site extends CI_Controller
{
    function __construct()
    {
        parent::Controller();
        $this->load->library('session');
        $this->load->helper('form');
    $this->load->helper('url');
    $this->load->model('membership/membership');
    }

  
  function register_form()
  {
       $this->load->view('membership/register_form');
  }

  function validate_data()
  {
  
  }

    function register_account()
    {
        $data = array(
            'email' => $this->input->post('email'),
            'username' => $this->input->post('username'),
      'password' => $this->input->post('password'),
      'confirm' => 'no',
        );
        
        $this->membership->add_record($data);
    $this->load->view('membership/register_success');
    }


/* These are function tests. */  
  function register_success()
  {
       $this->load->view('membership/register_success');
  }


}
//end of class