I have copied and pasted the iframe link from my map. When I paste it into a fairly simple html file with little or no css(Click this to see it work as expected).
HTTP Status 404 - type Status report message descriptionThe requested resource () is not available. Sun GlassFish Enterprise Server v2.1
You can click the links above to see the result. In the end the exact same page is being served. First with no wrapper and second wrapped in a lot of site context.
I can view both sites...and am not seeing any error messages. I'm not sure what the problem is for you. Perhaps you can provide more information on how to reproduce the error.
I found the issue. My PHP script which wrapped the html was changing the question mark (?) in the url to an ampersand (&). I probably fixed the php script before you looked at it.