I need help,it's not working

Hello,
Firstly I am sorry about my English.
I learn Flash by this great wesite, and i do everything according to the tutorial, but it’s not working.
I tried to do this lesson:
http://www.kirupa.com/developer/mx2004/motion_tween.htm
the 3 lesson of flash.
I finished everything, but the square don’t move right and left concertedly ,like in the tutorial.
maybe I need to do something that don’t mentioned in the tutorial?
i hope you can understand me, and thank you.