CodeIgniter自动加载form_validation导致模型文件错误

我使用codeigniter的form_validation库来验证我的应用程序中的表单。库加载在这里:

$autoload['libraries'] = array('database','form_validation');

自从包含库以来，我无法在应用程序中加载任何模型。我在浏览器中得到以下错误。该表单是用户注册到站点的注册表单。表单被完美地验证了。

 A PHP Error was encountered
 Severity: Notice
 Message: Undefined property: register_model::$load
 Filename: libraries/Form_validation.php
 Line Number: 147

下面是我尝试加载模型的函数:

  public function validateRegForm(){
    $this->load->model('register_model');
    $this->load->helper('url');
    $this->load->helper('form');
    $this->form_validation->set_rules('firstname', 'First Name', 'required');
    $this->form_validation->set_rules('lastname', 'Last Name', 'required');
    $this->form_validation->set_rules('address', 'Address', 'required');
    $this->form_validation->set_rules('email', 'Email', 'required');
    $this->form_validation->set_rules('phone', 'Phone', 'required');
    $this->form_validation->set_rules('username', 'Username', 'required');
    $this->form_validation->set_rules('password', 'Password', 'required');
    $this->form_validation->set_rules('confirm-password', 'Confirm Password', 'required|matches[password]');
    if ($this->form_validation->run() == FALSE){
     $data['title'] = 'Sign Up';
     $this->load->view('template/header', $data);
     $this->load->view('template/navigation');
     $this->load->view('register_view');
     $this->load->view('template/footer');
    } else {
      $data = array(
        'firstName' => $this->input->post('firstname'),
        'lastName' => $this->input->post('lastname'),
        'address' => $this->input->post('address'),
        'email' => $this->input->post('email'),
        'phone' => $this->input->post('phone'),
        'username' => $this->input->post('username'),
        'password'=> $this->input->post('password')
      );
      $this->register_model->insertUsers($data);
    }
}

注册模型文件:

 <?php
 class register_model extends CI_Controller {
 //Insert a new user to users table when registration form submits
   function insertUser(){
     $query = $this->db->query();
   }
}
?>

任何帮助都是感激的:)