While testing some updates to one of our Facebook applications today, I ran into an odd error message on IE8. The error message mentioned KB927917, and is caused by trying to modify the DOM before it is built. At first, I was confused, because the app is not modifying the DOM at all, its a redirect that is part of the authentication step. The culprit code was something like:

<script type="text/javascript">
top.location.href = 'http://example.com/foo/';
</script>

This was working, without warnings, in Chrome, Firefox, and IE7. To prevent IE8 from complaining, the redirect should happen after the page is done loading.

<script type="text/javascript">
window.onload = function() { 
    top.location.href = 'http://example.com/foo/'; 
};
</script>