"Array index is out of range" for any index value, when array.length>index

Like the title says, I always get an "array index out of range" error, even though the index I'm using is zero (for example) and the array has a length of 4 (or whatever). I'm utterly confounded. This is too simple to not work...

Here is the Code: (error line about 3/4 of the way down)

     var planetsInRouteOrder : GameObject[]; // This oughta' hold 'em.
 planetsInRouteOrder = new GameObject[numPlanets]; // numPlanets will be, for example, 4
 Debug.Log(planetsInRouteOrder.Length); // This checks out just fine.
 var planetsUnityArray = new Array(); // This will hold the ones we're checking
 var anglesUnityArray = new Array(); // Same deal ^ but for angles
 var planetsBuiltinArray : GameObject[]; // Builtin versions to let me reference their values...
 var anglesBuiltinArray : float[];
 
 
 
 for (i=0; i<numPlanets; i+=1) { // Add just the planets we're using this game, to the Arrays
     planetsUnityArray.Add( listOfPlanets[i] );
     anglesUnityArray.Add( anglesToPlanets[i] );// (and add their angles)
 }
 
 var highestSoFar : float;
 var indexOfHighest : int;
 var addedSoFar : int = 0;
 while (planetsUnityArray.length > 0){ // Until the Array is Empty
         
     planetsBuiltinArray = planetsUnityArray.ToBuiltin(GameObject); // Convert to Builtin so we can Reference their Values
     anglesBuiltinArray = anglesUnityArray.ToBuiltin(float);
 
     highestSoFar = -1; // Reset these
     indexOfHighest = -1;
     for (i=0; i<planetsUnityArray.length; i+=1) { // Find Highest Angle Still In Array
         if (anglesBuiltinArray[i] > highestSoFar){ // Update highest
             highestSoFar = anglesBuiltinArray[i];
             indexOfHighest = i;
         }
     }
         // Add to Ordered List and Remove it from both arrays
     //planetsInRouteOrder.Add( planetsBuiltinArray[i] );
     Debug.Log("Added so Far: "+addedSoFar.ToString());
     planetsInRouteOrder[addedSoFar] = planetsBuiltinArray[i]; // ERROR IS HERE - Even a hard coded index causes an out of range error. But using the current index always fails at zero.
     addedSoFar +=1;
     
     planetsUnityArray = new Array(planetsBuiltinArray); // Convert Back so we can Remove.
     anglesUnityArray = new Array(anglesBuiltinArray);
     
     planetsUnityArray.RemoveAt(i);
     anglesUnityArray.RemoveAt(i);
 }