Hi Rob,

"Access denied" error means that user's browser feels that it is unsafe for the main page to fiddle around the IFrame'd page. This security setting is not possible to overwrite, unfortunately. (Or, actually, fortunately, just not for IFrame designers :) )

This condition occurs when the domain of the main page is different from the domain of the included page. So, you can't IFrame yahoo.com into your site's page and have it autosize for you.

WARNING: mysite.com and www.mysite.com are considered DIFFERENT domains for this security issue. To avoid the problem 100% of the time, you should really just use a relative path, but that is not available with the current version of IFrame module. We will include this in the next version, of course.

The reason you haven't see it before is because it only happens when client-side script tries to snoop around a page displayed in IFRAME. So, when you selected auto height, you effectively invoked a client-side Javascript code that attempts to load the structure of the IFRAME'd document and check the height of it. It can do countless other things, but here it just does that. As soon as such an attempt is made, browser checks if it should allow Javascript to see that documents structure.

So, as you can see, unless you actually have some kind of client-side script doing these sort of things, you wouldn't encounter the issue. Since it's not super common - you haven't seen it yet.

We will try to implement some watch dogs in the future that would signal a developer of the site that they are going to have this problem. But for now... it's just me :)