Callback doesn't work, what's wrong?

[eluser]ReyPM[/eluser]
Still not working :-( my code now look like this:

Code:

public function check_unesco($value) {
if ($value == "0") {
     $this->form_validation->set_message('check_unesco', 'Debe seleccionar un Código UNESCO');
     return FALSE;
} else {
     return TRUE;
}
    }

And I test as:

Code:

<?php echo form_error('check_unesco'); ?>