When a page has become corrupted, the best thing to do is restore a backup of that page.
(1) Go to another, working page of the site, preferably in the same area/category/subcategory as the corrupted page.
(2) Click "[edit this page]".
(3) Click "Show Pages".
(4) If you are NOT in the same area/category/subcategory as the corrupted page, click on the appropriate link now to change area/category/subcategory.
(5) Click "Show auto backups: Restore an old page".
(6) Look for the name of the corrupted page. Choose the version with the latest date. Click the green "Restore Page" icon next to the page you want to restore.