SELECT e.id,e.title,e.date_added,u.first_name,u.last_name,u.username,e.file FROM media e LEFT JOIN users u ON u.id=e.modified_by LEFT JOIN media2siteCategories r ON r.id=e.id WHERE   e.published=1  GROUP BY e.id ORDER BY e.id DESC  LIMIT 5

This may be because database tables need to be updated.