Sorry to jump in, but I figured I would throw up a post also...
I just installed a fresh version of 4.3.4 and the IFRAME is getting me that error also if I want to use custom dynamic querystring parameters (like user id).
But if you don't need those, which I assume most do, you can add static ones right into the URL and that seems to work ok.
But I definitely need the dynamic parameters, so does anyone know if there is a fix?
I have the source version on my dev server and the install version on my production server, so I can recompile the solution on my dev server if needed.
Thanks very much in advance!