If you, by mistake, instead of closing a footnote macro open a new one, the page cannot be viewed. That's not much of a problem for normal pages. You just open the wiki editor and fix the syntax. On AWM pages with WYSIWYG editor configured for the text fields it's a very nasty problem. You have to change the class definition to use wiki editors (can only be done my the admin, not the user who edited the page), fix the syntax and roll back the class definition.