This example will give you the error you got, because Green is a string:

var myArray:Array = new Array("Green");
var objClass:Class = myArray[0] as Class;
var objisplayObjectContainer = new objClass() as DisplayObjectContainer;
addChild(obj);

Changing the first line will correct the mistake:
var myArray:Array = new Array(Green);

Probably the array members are all strings.