Codeigniter ion auth password problem

Code:
// signup

   function signup()

   {

         loggedIn();



         $this->load->view('partials/header');



         $this->form_validation->set_rules('username', 'Username', 'required');

         $this->form_validation->set_rules('password', 'Password', 'required|min_length[4]');

         $this->form_validation->set_rules('repassword', 'Retype Your Password', 'required|min_length[4]|matches[password]');



         if($this->form_validation->run() !== FALSE)

         {

            $username = $this->input->post('username');

            $password = $this->input->post('password');

             $email = $this->input->post('email');

            $additional_data = array(

               'name' => $this->input->post('name')

         );    

         $group = array('2');

         $this->ion_auth->register($username, $password, $email, $additional_data, $group);

         }



         $this->load->view('user/user_signup_view');

         $this->load->view('partials/footer');

   }