CiviMailer permalink permission denied in Joomla 2.5

When clicking on a public listed mailing a site visitor cannot see the mailing: they get a permission error from civi

Back trace:
home/domainxx/public_html/administrator/components/com_civicrm/civicrm/CRM/Core/Error.php, backtrace, 303
/home/domainxx/public_html/administrator/components/com_civicrm/civicrm/CRM/Utils/System/Joomla.php, fatal, 502
/home/domainxx/public_html/administrator/components/com_civicrm/civicrm/CRM/Utils/System.php, permissionDenied, 185
/home/domainxx/public_html/administrator/components/com_civicrm/civicrm/CRM/Core/Invoke.php, permissionDenied, 147
/home/domainxx/public_html/components/com_civicrm/civicrm.php, invoke, 79
/home/domainxx/public_html/components/com_civicrm/civicrm.php, civicrm_invoke, 24
/home/domainxx/public_html/libraries/joomla/application/component/helper.php, require_once, 388
/home/domainxx/public_html/libraries/joomla/application/component/helper.php, executeComponent, 357
/home/domainxx/public_html/includes/application.php, renderComponent, 187
/home/domainxx/public_html/index.php, dispatch, 42

Original forum post here http://forum.civicrm.org/index.php/topic,22942.msg99481.html#msg99481