Gpf_Rpc_Form::setFieldError PHP Method

        public function setFieldError($name, $error)
        {
            $this->isError = true;
            $record = $this->fields->getRecord($name);
            $record->set(self::FIELD_ERROR, $error);
        }

 /**
  * @return boolean
  */
 public function validate()
 {
     $errorMsg = false;
     foreach ($this->validators as $fieldName => $fieldValidator) {
         if (!$fieldValidator->validate($this->form->getFieldValue($fieldName))) {
             $errorMsg = true;
             $this->form->setFieldError($fieldName, $fieldValidator->getMessage());
         }
     }
     if ($errorMsg) {
         $this->form->setErrorMessage($this->_('There were errors, please check highlighted fields'));
     }
     return !$errorMsg;
 }