flash actionscript: Hi,

I can't seem to work get this script to perform an action when the OK button
is pressed. And, no matter what I do I can't get an alert box to display YES
and NO. It only ever displays yes. Can anyone see anything wrong with the
attachedcode?

send_btn.onRelease = function() {
question = "Please use the secure payment window to make your payment.";
_root.mxca.show(question, "Payment Process", Alert.OK, null,
alertClickHandler);
}
var alertClickHandler:Function = function (evt_obj:Object) {
switch (evt_obj.detail) {
case Alert.OK :
question = "Was the payment successful? (If the payment was not successful
and you continue, the order will be cancelled.";
_root.mxca.show(question, "Payment Successful?", Alert.YES | Alert.NO, null,
payClickHandler);
}
};
var payClickHandler:Function = function (evt_obj:Object) {
switch (evt_obj.detail) {
case Alert.YES :
trace("yes");
break;
case Alert.NO :
trace("no");
break;
}
};

PLEASE HELP :(