Stop yoyo

Hi!
I have had this question in ActionScript.org Forum but didn´t get any answers so I try again here in Kirupa.
I have this code which is working alright.

var myx_tween:Object = new Tween(jojjox, "_x", Regular.easeIn, jojjox._x, jojjox_end._x, 3, true);
var myy_tween:Object = new Tween(jojjox, "_y", Regular.easeIn, jojjox._y, jojjox_end._y, 3, true);
myy_tween.onMotionFinished = function() {
myx_tween.yoyo();
myy_tween.yoyo();
};

Now I want the yoyo to stop when I press a button. I have tried with
myx_tween.stop();
myy_tween.stop();
but it doesn´t work. If someone knows how to stop it I would be quit happy.