Using addChild with a variable

Okay, I am trying to use addChild on a current project I am working on, the only problem is that I have to add movieclips to the stage based on an array of movieclips given to me and a number (index).

At this point I am trying it like so:

var array:Array = new Array('Mc1', 'Mc2', 'MC3'); // etc.
var num:Number = 1;
addChild(array[num]);

I have exported all of my movieclips for actionscript and in the first frame.

The only issue that I am getting an error:

TypeError: Error #1009: Cannot access a property or method of a null object reference.

and am not sure quite how to resolve it.

Any help would be greatly appreciated.
BetaWar