IE6 secure and nonsecure error - nothing in Fiddler/no iframes

I've got the issue of IE6 showing the "secure and nonsecure it开发者_如何学Pythonems" 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

I had this problem, and everywhere I found iframes listed to be a common cause so I did not think to check my regular frames. It turns out IE6 considers a frame without a src to be nonsecure as well as an iframe.

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.