Is that not the message that appears when in system preferences the site is set to be closed? Did you check that preference? You can still connect with /user.php, and have access tothe backoffice with /admin.php, isn't it?
The module (Random client Quotes?) was written for PHP4 and you are probably on PHP5. Replace all occurences in all files of HTTP_*_VARS to _* (eg HTTP_GET_VARS to _GET).