The referrer string is not being downloaded with the order.

[KB]

This can happen when 'SSL for login and checkout pages only' option is selected and the http and secure server use different server names.

This problem can be resolved by uploading referrer.pl to the cgi-bin on the secure server instead of to the normal cgi-bin. Remember to set the permissions to (755 on Unix) and to adjust the links to the referrer.pl.