Password Confirmation in zend framework

I add this class to library/My/Validate/PasswordConfirmation.php ``` <?php require_once 'Zend/Validate/Abstract.php'; class My_Validate_PasswordConfirmation extends Zend_Validate_Abstract { const NOT_MATCH = 'notMatch'; protected $_messageTemplates = array( self::NOT_MATCH => 'Password confirmation does not match' ); public function isValid($value, $context = null) { $value = (string) $value; $this->_setValue($value); if (is_array($context)) { if (isset($context['password']) && ($value == $context['password'])) { return true; } } elseif (is_string($context) && ($value == $context)) { return true; } $this->_error(self::NOT_MATCH); return false; } } ?> ``` then I create two field in my form like this : ``` $userPassword = $this->createElement('password', 'user_password'); $userPassword->setLabel('Password: '); $userPassword->setRequired('true'); $this->addElement($userPassword); //create the form elements user_password repeat $userPasswordRepeat = $this->createElement('password', 'password_confirm'); $userPasswordRepeat->setLabel('Password repeat: '); $userPasswordRepeat->setRequired('true'); $userPasswordRepeat->addPrefixPath('My_Validate','My/Validate','validate'); $userPasswordRepeat->addValidator('PasswordConfirmation'); $this->addElement($userPasswordRepeat) ``` everything is good but when i submit form always I get the 'Password confirmation does not match' message ? What's Wrong in my code