form_validation doesn't show errors

Hi!

I have problem with Form Validation from CI 3.0 RC2.
I have method in controller:

PHP Code:

public function dodaj()
 {
// ...
 if ( !empty( $_POST ) )
 {
 
 $this->form_validation->set_rules('imie_wolont', 'Imie wolontariusza', 'trim|required');
 $this->form_validation->set_rules('d_imie_wolont', 'Drugie mie wolontariusza', 'trim|required');
//etc 

 if ($this->form_validation->run() == TRUE) {
 
 $dodaj_wolont = array(
 'imie' => $this->input->post( 'imie_wolont' ),
 'drugie_imie' => $this->input->post( 'd_imie_wolont' ),
// etc
 );

 $this->Wolontariusze_model->dodaj( 'wolontariusze' , $dodaj_wolont );
 }
 } 


and view with:

PHP Code:

echo validation_errors(); 


but i don't getting errors, why? (I have form and form_validation in autoload)