set_message Dysplay

[eluser]Gabi3xz[/eluser]
Example
have code

Code:

$this->load->library('form_validation');

if ( $res !== false ) {
    $_SESSION['username'] = $this->input->post('email_address');
    //insert here set_message "Success"
    $this->form_validation->set_message('success_login', 'Login success');

            } else {
    echo "Incorrect";
   }

used

Code:

$this->form_validation->set_message('success_login', 'Login success');

and added $lang['success_login'] = "Success login."; in form validation lang and does not display message.
What is not correct?