Why does this JavaScript cause a "Permission Denied" error in IE

The following code throws a Permission Denied error in IE, citing jQuery (1.6.2) line 6244 Char:2:

function addAgreement() {
    var url = window.location.toString();
    var pieces = url.split('/');
    var site_url = url.replace(pieces[pieces.length -1], '');
    $('.login').append('<div id="dialog"></div>');
    $('#dialog').load(site_url + '?page_id=443');
}

$('#dialog').dialog({
    width: 800,
    position: 'top',
    modal: true,
    buttons: {
        "Agree": function() { 
            agreed = true;
            var val = $('#registerform').attr('action') + '&agreed=1';
            $('#registerform').attr('action', val);
            $(this).dialog("close");
            $('#registerform').trigger('submit');
        }, 
        "Disagree": function() { 
            agreed = false;
            $(this).dialog("close"); 
        } 
    }
});

It works in Firefox — is this som开发者_开发技巧ething to do with same origin policy? jQuery is being served by Google CDN.

UPDATE The content being loaded is a WordPress page which also contains includes for cufon-yui.js (served locally). I have tried serving jQuery locally too (i.e not from the Google CDN) and this made no difference.

UPDATE 2 Removing the following script tags from the loaded page stops the error from appearing.

<script type='text/javascript' src='<?php echo bloginfo('template_url') ?>/inc/js/cufon-yui.js'></script> 
<script type='text/javascript' src='<?php echo bloginfo('template_url') ?>/inc/js/path/to/font.js'></script>
<script type='text/javascript'>
Cufon.replace('#page')('.title');
</script> 

For AJAX requests, www. is seen as a sub-domain and breaks the same-origin policy for the xmlhttprequestobject. Make sure the domain in your AJAX request matches the domain of the page and your javascript file.