External Interface not working in IE7

programming flash
1

I’m having a problem with Flash and Internet Explorer. I’m trying to close out a browser window with

//as code
ExternalInterface.call(“closeWindow”);

//js code
function closeWindow(){
alert(‘hey’);
window.close();
}

Of course this works in all other browsers except IE, the error that I am getting is:
‘null’ is null or not an object

any ideas? thanks