i don't think broadcastermx is an as2 (or as3) class.
As I said, this movie was compiling correctly in Flash CS4 using ActionScript 2
BroadcasterMX.as is called from Tween.as. If you have Flash installed in your machine you can go to your user files path and then to Adobe\Flash CS5\es_ES\Configuration\Classes\mx\transitions and you will find it there (maybe you have to replace es_ES by en_US or whatever your install language is)
any other more helpful answer?
Anyhow, I would be insterested in any other code that moves the clip from the bottom of the screen where it is to the top in two seconds while the rest of the movie keeps running. (the original code did more things and also moved the clip in the x coordinates and changed size and opacity, so there were 4 tweens and several other objects that also Tweened in and by the stage)
Here is the code reduced even more (just to discard the easing methods as cause of the error):
new Tween(MCcore, "_y", null, 500, 0, 2, true);