CakePHPform checkbox validation error not shown, but input error - validation

Question

I have a form with required fields, one field is a checkbox. All validation errors will be shown, but no error from checkbox field. I installed DebugKit-Plugin and see, that there will be a validation error, but the message wouldn't shown.
class Users extends AppModel {
public $name = 'Users';
public $validate = array(
'email' => array(
'notEmpty' => array(
'rule' => 'notEmpty',
'message' => 'Bitte geben Sie ihre Email-Adresse ein',
'allowEmpty' => false,
),
'isUnique' => array(
'rule' => 'isUnique',
'message' => 'Diese Adresse ist bereits angemeldet',
),
'email' => array(
'rule' => array('email',true),
'message' => 'Bitte geben Sie eine gültige Email-Adresse ein',
'allowEmpty' => false,
),
),
'terms' => array(
'rule' => array('comparison','!=',0),
'message' => 'Sie müssen unseren Nutzungsbedingungen zustimmen',
'allowEmpty' => false,
),
);
}
Form:
<div class="right text-right" id="register_form">
<?php
echo $this->Form->create('Users', array('action' => 'register', 'inputDefaults' => array()));
echo $this->Form->input('gender', array('label' => 'Anrede: ', 'class' => 'inputField', 'options' => array('m' => 'Herr', 'f' => 'Frau')));
echo $this->Form->input('first_name', array('label' => 'Vorname: ', 'class' => 'inputField'));
echo $this->Form->input('last_name', array('label' => 'Nachname: ', 'class' => 'inputField'));
echo $this->Form->input('email', array('label' => 'Email: ', 'class' => 'inputField'));
echo $this->Form->input('terms', array('div' => true, 'type' => 'checkbox', 'value' => 0, 'label' => false, 'before' => ' <label for="UsersTerms">Ich akzeptiere die '.$this->Html->link('AGB', array('controller' => 'pages', 'action' => 'terms')).' </label>'));
echo $this->Form->submit('Anmelden', array('class' => 'button'));
echo $this->Form->end();
?>
</div>
Controller:
public function register() {
if ($this->Auth->user())
$this->redirect($this->referer('/'));
if ($this->request->is("post")) {
$this->Users->create();
$this->Users->set(Sanitize::clean($this->request->data));
#if ($this->Users->validates())
# die(debug($this->Users->validationErrors));
$this->_hash = $this->Auth->password($this->Users->data['Users']['email']);
$this->_password = $this->__randomString(8, 8);
$this->Users->set('password', $this->Auth->password($this->_password));
if ($this->Users->save()) {
$this->Users->id = $this->Users->getLastInsertID();
$this->_sendActivationMail();
$this->Session->setFlash('An die angegebene Emailadresse wurde soeben ein Aktivierungslink versendet.', 'default', array('class' => 'yellow'));
$this->redirect($this->referer());
} else {
$this->Session->setFlash('Ein Fehler ist aufgetreten', 'default', array('class' => 'red'));
}
}
}
I tried with a "$this->Form->error('terms');" but when I debug this line, in case of error there will be only
<div class="error_message"></div>
CakePHP is last version. Searching since 4 hours for help, but google has no answer. Have you?
Greetings
M.

Answer 1

If anyone has same problem, i could solve mine:
Problem was special char "ü". I tried to save my file with ISO 8859-1 but it needed to save with UTF8. Now error message will be shown.