need help with logout javascript on non-vb page

[Slapyo]

here is the javascript just above the logout link:

<script type="text/javascript">
<!--
	function log_out() {
		ht = document.getElementsByTagName("html");
		ht[0].style.filter = "progid:DXImageTransform.Microsoft.BasicImage(grayscale=1)";
		if (confirm('Are you sure you want to log out?')) {
			return true;
		} else {
			ht[0].style.filter = "";
			return false;
		}
	}
//-->
</script>

here is my logout link:

(<a href="http://www.mysite.com/forums/login.php?do=logout&u=<?=$userid?>" onclick="return log_out()">Logout</a>)

i copied and pasted everything straight from vB. my problem is the page doesn't go grayscale like when i logout inside the forums. i don't know what the problem is, because it works just fine inside the forums. it just doesn't work on a non-vb page. any help is appreciated.