Can't load class 'mx.transitions.BroadcasterMX'

Question

I have a flash piece that I programmed last year in CS4 and now I had to change a little bit of the content, nothing code related, just modify an image. Now I'm using CS5 but when I try to publish the movie, I get an error: Can't load class or interface 'mx.transitions.BroadcasterMX' (I'm translating fom spanish)
I have reduced the fla to the minimal expression. just a frame with the following AS:
import mx.transitions.Tween;
import mx.transitions.easing.*;
new Tween(MCcore, "_y", None.easeNone, MCcore._y, 0, 2, true);
stop();
Where MCcore is just a square in the bottom of the screen that should move to the top.
I've checked that BroadcasterMX is in the correct path of the hard drive and is not corrupted.
I've tried with several publishing options from flash player 6 to flash player 10 but always the same error.
As I said, the movie compiled correctly in CS4. What is going wrong?

Answer 1

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)