This tip was given to us by one of our customers so I thought I would pass it along for everyone:

If you happen to be using google analytics with osCommerce, the analytics script can invalidate the SSL (typically shown as a broken lock in the browser). To fix this simply change 'http://www.google-analytics.com' to 'https://ssl.google-analytics.com' Alternately you could disable google analytics when in SSL with the following <?php } if ($request_type != 'SSL') { ?> Insert google analytics code here. <? } ?>