code: protected void registerTagError(String message, Throwable e)
              throws JspException
      {
          System.err.println("Error in rendering tree:" + message);
          logger.error(message, e);
      }
docs: Errors during rendering will call through this method.  During the XmlHttpRequest, these
  will just be logged and we will go on.
  @param message
  @param e
  @throws JspException