I’ve got the issue of IE6 showing the “secure and nonsecure items” error on an SSL page. Looking into it though none of the usual causes seem to apply. There are no calls to http://, there are no iframes in the page, fiddler and httpfox both show only requests to https:// – what else can i check?
In Firefox and IE there is nothing to suggest there is mixed content at all
There are some strange bugs in IE6-IE8 where you will get mixed content alerts from things that have nothing to do with it at all, such as javascript. For example, on the Air Canada website, you will see this happen.