Your board URL incorrectly contains a trailing "/".
The description for this XenForo setting specifically says 'Do not include a trailing "/" or "index.php".' By including one, you break most links that will rely on this to create absolute links.
While some sites can easily recover from this (try adding a double-slash on this page), inserting a double slash in place of a single slash on XenForo results in the page not being found.