Button affecting Movie Alpha

Question

I have 2 buttons on my stage and also 2 movies. The 2 movies
are an existing animation and a proposed animation, the existing
movie clip is directly on top of the proposed. When I click the
Proposed button I want that movies alpha to be 100 while the
existing goes to zero. And vice versa. Right now, I can get that to
work, however, I can't reverse it and click to existing button to
get the existing movie to 100 and make the propsed 0.
Here's my script:
PropButton.onRelease = function(){
MovieExist._alpha = 0;
MovieProp_alpha = 100;
ExistButton.onRelease = function(){
MovieProp._alpha = 0;
MovieExist_alpha = 100;
}

Answer 1

It's not working for some reason. The first 2 still work but
the new Summer movie never shows up.
PropButton.onRelease = function(){
SharpExist._alpha = 0;
SharpSummer._alpha = 0;
SharpProp._alpha = 100;
ExistButton.onRelease = function(){
SharpProp._alpha = 0;
SharpSummer._alpha = 0;
SharpExist._alpha = 100;
SummerButton.onRelease = function(){
SharpProp._alpha = 0;
SharpExist._alpha = 0;
SharpSummer._alpha = 100;
}