php - CodeIgniter Auto Loading form_validation causes Error with Model files

I am using CodeIgniters form_validation library to validate a form in my app. Library loaded here:

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

Ever since including the library I cannot load any models in the app. I get the following error in my browser. The form is a registration form for users to sign up to the site. The form gets validated perfectly.

 A PHP Error was encountered

 Severity: Notice


 Message: Undefined property: register_model::$load

 Filename: libraries/Form_validation.php

 Line Number: 147

Here is my function that tries to load the model:

  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);
    }
}

Register model file:

  class register_model extends CI_Controller {

 //Insert a new user to users table when registration form submits
   function insertUser(){

     $query = $this->db->query();

   }


}

?>

Any help is appreciated :)