problem with ExternalInterface class

[absolutezero342]

ok, here's my AS3 code:

if (ExternalInterface.available)
{
    // Perform ExternalInterface method calls here.

	var banner_width:Number = ExternalInterface.call("getWidth");
	//var banner_width:Number = 500;
	ExternalInterface.call("trace", banner_width);
}

and here's my Javascript:

function getWidth() {
	var banner_width = 600;
	return banner_width;
}

function trace(val) {

	alert(val + ' = width');
}

this works in FF and outputs 600 like expected and it doesn't work in IE, instead it outputs 0??? why is this handled differently in different browsers?
thanks in advance!