Error on validation related model

I am trying to save a model and a related one. But when I execute save() on parent, it fires a error from related model validation.

Related model validation:

    public function validation()
    {
      if(!$this->getName())
      {
        $this->appendMessage(new \Phalcon\Mvc\Model\Message('Invalid Name'));
      }

Error:

Invalid message format 'string'

Why it's not appending the right message? If I remove validation both are saved properly.