Logout through XMLHTTPRequest Object is not working in Opera

I am using the basic authentication mechanism for my website in IIS. To logout the user I am using something similar to this JavaScript function:

[CODE]
function logoutUser() {
setTimeout(‘location.reload(true)’, 1000);
xmlhttp = GetXmlHttpObject();
if (xmlhttp==null) {
return;
}
//alert(xmlhttp);
var url = “index.php”;

xmlhttp.open(“GET”, url, true, “dummy_user”, “dummy_password”);

xmlhttp.setRequestHeader( “If-Modified-Since”, “Sat, 1 Jan 2000 00:00:00 GMT” );
xmlhttp.setRequestHeader( ‘Accept’, ‘message/x-formresult’ );
xmlhttp.send(null);
}

function GetXmlHttpObject()
{
if (window.XMLHttpRequest)
{
// code for IE7+, Firefox, Chrome, Opera, Safari
return new XMLHttpRequest();
}
if (window.ActiveXObject)
{
// code for IE6, IE5
return new ActiveXObject(“Microsoft.XMLHTTP”);
}
return null;
}

[/CODE]

The idea is to force a request with some invalid credentials, in order to invalidate the real credentials cached by the browser.

It is working fine in IE,Firefox, Safari, Google Chrome but not in Opera.

Please help me in this regard.

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