Tween class with onEnterFrame

I put a movieclip I created (located in the library) on the stage with AS, then dynamically drew a white box on top of it. The tween is meant to fade the the white box to 0, but…nothing! Anybody see some syntax errors I’m missing?

ActionScript Code:
[FONT=Courier New][LEFT][COLOR=#0000FF]stop[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000000])[/COLOR];

[COLOR=#0000FF]import[/COLOR] mx.[COLOR=#000080]transitions[/COLOR].[COLOR=#000080]Tween[/COLOR];
[COLOR=#0000FF]import[/COLOR] mx.[COLOR=#000080]transitions[/COLOR].[COLOR=#000080]easing[/COLOR].*;

[COLOR=#808080]//White box (for use in transitions)[/COLOR]
[COLOR=#0000FF]this[/COLOR].[COLOR=#0000FF]createEmptyMovieClip[/COLOR]COLOR=#000000[/COLOR];
transBox.[COLOR=#0000FF]moveTo[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000080]0[/COLOR], [COLOR=#000080]0[/COLOR][COLOR=#000000])[/COLOR];
transBox.[COLOR=#0000FF]beginFill[/COLOR]COLOR=#000000[/COLOR];
transBox.[COLOR=#0000FF]lineTo[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000080]1280[/COLOR], [COLOR=#000080]0[/COLOR][COLOR=#000000])[/COLOR];
transBox.[COLOR=#0000FF]lineTo[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000080]1280[/COLOR], [COLOR=#000080]800[/COLOR][COLOR=#000000])[/COLOR];
transBox.[COLOR=#0000FF]lineTo[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000080]0[/COLOR], [COLOR=#000080]800[/COLOR][COLOR=#000000])[/COLOR];
transBox.[COLOR=#0000FF]lineTo[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000080]0[/COLOR], [COLOR=#000080]0[/COLOR][COLOR=#000000])[/COLOR];
transBox.[COLOR=#0000FF]endFill[/COLOR];

[COLOR=#0000FF]this[/COLOR].[COLOR=#0000FF]attachMovie[/COLOR][COLOR=#000000]([/COLOR][COLOR=#FF0000]“gradient”[/COLOR], [COLOR=#FF0000]“colorGrad”[/COLOR], [COLOR=#000080]1[/COLOR][COLOR=#000000])[/COLOR];

[COLOR=#0000FF]this[/COLOR].[COLOR=#0000FF]onEnterFrame[/COLOR] = [COLOR=#000000]function[/COLOR]COLOR=#000000[/COLOR] [COLOR=#000000]{[/COLOR]
[COLOR=#000000]var[/COLOR] transTween:Tween = [COLOR=#000000]new[/COLOR] Tween[COLOR=#000000]([/COLOR]transBox, [COLOR=#FF0000]"_alpha"[/COLOR], Strong.[COLOR=#000080]easeOut[/COLOR], [COLOR=#000080]100[/COLOR], [COLOR=#000080]0[/COLOR], [COLOR=#000080]1[/COLOR], [COLOR=#000000]true[/COLOR][COLOR=#000000])[/COLOR];
transTween.[COLOR=#000080]onMotionFinished[/COLOR] = [COLOR=#000000]function[/COLOR]COLOR=#000000[/COLOR] [COLOR=#000000]{[/COLOR]
[COLOR=#0000FF]delete[/COLOR] [COLOR=#0000FF]this[/COLOR].[COLOR=#0000FF]onEnterFrame[/COLOR]COLOR=#000000[/COLOR];
[COLOR=#000000]}[/COLOR]
[COLOR=#000000]}[/COLOR]
[/LEFT]
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