Argument out of range - Generic list (JS)

I'm using a class to organize many arrays into an object. Then using that object to tell my game what to do at certain stages. This error is thrown ArgumentOutOfRangeException: Argument is out of range and I have no idea why. Here's my code for accessing the list:

 import System.Collections.Generic;
 
 var skin: GUISkin;
 
 function OnGUI() {
     GUI.skin=skin;
     var item = Stage.Stages[0];
 }

And this is my code for the stage class:

 import System.Collections.Generic;
 
 class Stage
 {
     var controlArray: String[];
     var taskName: String[];
     var taskStatus: Texture2D[];
     var PC: boolean;
     var arrowArray: GameObject[];
 }

 //what a stage object might look like
 var Stage16 = new Stage();
 Stage16.controlArray[0] = "";
 Stage16.taskName[0] = "findTheWaterCooler";
 Stage16.taskName[1] = "returnToYourDesk";
 Stage16.taskName[2] = "dropToTheGround";
 Stage16.taskName[3] = "coverUnderTheDesk";
 Stage16.taskName[4] = "holdDuringTheEarthquake";
 Stage16.taskName[5] = "dustYourselfOff";
 Stage16.taskStatus[0] = Resources.Load("check_box_checked");
 Stage16.taskStatus[1] = Resources.Load("check_box_failed");
 Stage16.taskStatus[2] = Resources.Load("check_box_checked");
 Stage16.taskStatus[3] = Resources.Load("check_box_checked");
 Stage16.taskStatus[4] = Resources.Load("check_box_checked");
 Stage16.taskStatus[5] = Resources.Load("check_box_empty");
 Stage16.PC = false;
 Stage16.arrowArray[0] = null;


 static var Stages : List.<Stage> = new List.<Stage>(21);
 Stages[0] = Stage0;
 Stages[1] = Stage1;
 Stages[2] = Stage2;
 .
 .
 //and so on

I don't understand why its giving me a index out of range error?? Please help!