Help making a button load a MC

Hey, Im creating a game in flash and i want to have it so that the button you click loads a MC from my library. I went into the properties of the MC and checked Export for Actionscripting, gave it an ID name and an instance name.

Heres the code i placed on the button:

my_btn.onPress = function() {
_parent.attachMovie('rainmovie', 'rain', _parent.getNextHighestDepth(), {_x:100, _y:100});
}

when i test the movie an error message pops up saying:

Statement must appear within on handler
my_btn.onPress = function() {

please help thanks!

I'm not going to take credit for this, as I just pulled it off of google for ya, but it should help:

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Yeah, Flash is just telling you that your code (attached to an MC) must be contained in one of the following clip events :

onClipEvent (enterFrame) {

//statement here

}

enterFrame can be replaced with, load, Unload, Mouse down, Mouse up, Mouse move, Key down, Key up, Data.