We'll have to look into why that notice is showing. That isn't a critical error message and normally shouldn't be shown on a production site. I'd recommend going to the Joomla Global Configuration area and setting Error Reporting to "System Default" or "None". That will hide any of these types of notices/warnings. Obviously, those messages should happen at all, and we'll get that fixed, but the above quick change should make things go away as well.
Thanks,
Alex