[CS3] this._root. or this._parent just won't work + retrieving a MC's y position.

Question

I've got some buttons which when i click them i want them to
make a particular MC move downwards. Well the thing is that when i
try to reference to that particular MC it just won't happen (yes
the MC has an instance name). For the button i tried something like
btn1.onRelease = function() {
var mcReferece = this._root.myMC;
trace(mcReference);
or
btn1.onRelease = function() {
var mcReferece = this._parent.myMC;
trace(mcReference);
since they have the same parent.
Both returned undefined.
I've also tried putting directly myMC in the tween, with no
effects whatsoever.
The second question is, how can i retrieve the y position of
a MC?
Also i've tried putting the tween on the MC itself...
onClipEvent(enterFrame){
import mx.transitions.Tween;
import mx.transitions.easing.*;
var myTween:Tween = new Tween(_level0.myMC, "_y",
Elastic.easeOut, 195, 545, 10, false);
But not only does it not animate it doesn't even go where
it's supposed to go...
Thanks in advance.
P.S. This might be rlly simple to solve but it's been bugging
me and can't go on without it. Couldn't figure it myself. Got rlly
annoyed at some point :|

Answer 1

The only 7 i can think of that i have in the project is what
comes after 6 (ridiculous i know... xD) :
for (i=1; i<=6; i++) {
var current_btn = this["btn"+i];
current_btn.onRollOver = function() {
var currentAlpha = this.cover_mc._alpha;
var myHoriTween:Tween = new Tween(this.cover_mc, "_alpha",
Strong.easeOut, currentAlpha, 0, 0.5, true);
current_btn.onRollOut = function() {
var currentAlpha = this.cover_mc._alpha;
var myHoriTween:Tween = new Tween(this.cover_mc, "_alpha",
Regular.easeIn, currentAlpha, 100, 0.5, true);
but that's just the animation for the individual buttons.