In dashboard (control panel) in front-end, if clicking on "Notification" and then make a page refresh (F5) this error occurs.
(0) Invalid controller: name='Notification', Format=''
The same thing happens on your demo page (logged in with user/user).
For full error message see attached file.
If the problem can be solved why worry?
If the problem can not be solved, worrying will do you no good.