Try going to another page so your dashboard bar shows up and then choosing "Dashboard->Full Sitemap". Click the offending page and choose "Versions". Delete the newest version by putting a check in the top version and click the 'garbage can' icon. Please note that the "admin" user always sees the most recent page version so you can't just leave this new (broken) version intact and approve an older version. You must delete the newest page version in order for the admin to access the older, non-offending version of the page.