ActionScript 3.0 :: Flash Dynamically Addressing An Existing MovieClip On Stage?

I am loading an external XML file. According to the information loaded from the file I would like to highlight a symbol (MovieClip) when I press a corresponding button. The Button and the MovieClip change every time I load a new XML, so it has to be dynamic.I tried the following, but that doesn't work, does anyone know why?I have an Array defined (a_HighlightArray) that I fill within a loop to hold the object (as a string! ) that is supposed to be highlighted when I press the corresponding button:

a_HighlightArray[i] = "o_Map.o_Privatwelt.o_Layer4";

Later, when I want to address the Symbol I am using the following (where Quest corresponds to the No of the button I pressed):

[a_HighlightArray[Quest]]gotoAndStop(2);

There is no error that comes up but it just doesn't do what expected. Strangely enough, if I address the Symbol directly it works perfectly fine:

o_Map.o_Privatwelt.o_Layer4.gotoAndStop(2);