Gpf_Rpc_Form::getFieldError PHP Method

        public function getFieldError($name)
        {
            $record = $this->fields->getRecord($name);
            return $record->get(self::FIELD_ERROR);
        }

    protected function checkUsernameIsValidEmail(Gpf_Rpc_Form $form, $operationType) {
        $username = $form->getFieldValue("username");
        $emailValidator = new Gpf_Rpc_Form_Validator_EmailValidator();

        if(Gpf::YES == Gpf_Settings::get(Gpf_Settings_Gpf::NOT_FORCE_EMAIL_USERNAMES) || $emailValidator->validate($username)) {
            return true;
        }

        $form->setFieldError("username", $this->_("Username must be valid email address"));
        $form->setErrorMessage($form->getFieldError('username'));
        return false;
    }