Cannot bring var to _root

This is the situation:
I have several MC´s into one another(4) and a button at the bottom of all of them.
The button is supposed to bring up a value contained into a textbox down there up to _root.textbox_variable

Like this:
on(press){
_root.top_textbox_variable=bottom_text_value;
{

But it doesnt work. It only works when I have the textbox one level below _root. like this:

on(press){
_root.MC.MC_textbox_variable=bottom_text_value;
{
As if I cannot go to _root but yes to _root.Sub
Any clue?
Thanks again for the help.

Because the variables exist inside the movie clips, you have to target them on the movie clips. The problem that you were having with your original script was that you were targeting variables on the main time line that don't affect anything inside your movieclips. Your second script is more correct. An alternative solution to get what you want is inside each movieclip have a script like so

Code:

---

onClipEvent(enterFrame) {
  myvar = _root.myvar;
}

---

This will pull the variables off the _root timeline and subsititute those variables into your movie clips.