Tweens and onMotionFinished in MX2004

I created some code in Flash 8 for a client using MX2004.

I used Tween and made a onMotionFinished function. I saved it as a MX2004 file, but when he tries to compile it he gets

[FONT=Verdana][SIZE=2][FONT=Verdana]**Error Scene=movie scene, layer=Actionscript, frame=1:Line 26: There is no property with the name ‘onMotionFinished’.[/FONT][/SIZE][/FONT]**
[FONT=Verdana][SIZE=2][FONT=Verdana] gallery.onMotionFinished = function() {[/FONT][/SIZE][/FONT]