Transparent Movie Clip Button

I’m new to flash and I’m trying to create a transparent movie clip button. This button cotains an animation in its timeline. The animation is based on tweening a series of pngs with alpha channels so they will have a transparent background. My intention is for the background of the HTML page to show through the alpha channels of both the Button (movie clip) and its animation. So far the pngs of the animation work fine (meaning they retain their transparency). I’ve also set up the flash window to windowless so it is all completely transparent.

The problem is in my mc button wich is also made out of a transparent png. The Button (movie clip) retains a white shadow behind my animation. Also if I set the button’s alpha property to zero it becomes transparent without the white shadow, but it erases my animation as well. Can anyone tell me how to get around this issue? In other words, can someone tell me how to create a transparent movie clip button that when activated will show an animation in it with transparency and without the white shadow? Thanks in advance.