Sitefinity iFrame parent.document.getElementByID not working

I have a Sitefinity page with a content block that has an iFrame that pulls in a sub-page from another asp.net site.

I want the iFrame on the Sitefinity page to resize based on the size of the sub-pages content to prevent the clumsy dual scroll bars when the sub-page is very tall.

The content block iframe is called "dynframe":
<iframe width="878" height="300" id="dynframe" src="http://subsite.contoso.com" frameborder="0" marginwidth="0" marginheight="0" scrolling="auto" vspace="0" hspace="0"></iframe>

And the sub-sites page contains:

<

body onload="resizeToContent()">....

And has this script block to to the work:

<Rad:RadCodeBlock ID="ResizeContentRadCodeBlock" runat="server">

<script type="text/javascript">

function resizeToContent()

if (self == parent) alert("self=parent!"); return false;

var x = 0;

var y = this.document.body.scrollHeight;

while (x < y) x += 1;

alert(

"resizing x=" + x);

var z = parent.document.getElementById('dynframe');

alert(

"after z!");

if (z != null) z.style.height = x; alert("dynframe height: " + x + " -> " + z.style.height);

else alert("dynframe not found!");

</script>

</Rad:RadCodeBlock>

When the page runs, it always shows the resizing x=? alert with the proper height we are trying to achieve.
BUT, it never reaches the alert("after z"); at all!
It's as if the var z = parent.document.getElementById('dynframe');
is stopping or blocking the script block from continuing, so
of course the work of setting the iFrame size cannot be done.

This iFrame resizing seems to be a common practice out there and works perfectly
other non-sitefinity tests I have tried so I am wondering if Sitefinity is purposely
blocking this in some way.

Frustrated, any help would be much appreciated!, Scott

As per usual, you figure it out just a fraction of a second after you give up and ask for help.
Turns out the getElementbyID was getting an Access Denied (cross-site scripting) Error since
the iFrame page was in another domain (actually a sub-domain). So that's the problem although
I don't have an answer yet as I can't seem to get a virtual directory underneath Sitefinity properly
configured and working as a separate application under IIS 7.5....sigh....