How to randomly generate pickups

This is driving me crazy. I'm trying to convert UnityScript to C# for a tutorial I'm working on. I got pretty far until I had to do arrays - something I haven't been good at since I started programming. I keep getting an error and don't know how to fix it. Here's my code:

  using UnityEngine;
     using System.Collections;
 
 
 public class PickupController : MonoBehaviour 
 {
     //the pickup prefab assigned via the Inspector
     public GameObject pickupPrefab;
     private GameObject spawnedPickup;
     
     //the number of pickups to have around the level at any one time
     public int numberOfPickups = 2;
     
     // the ARRAY of spawnpoints that our pickup will be spawned at
     private GameObject[] spawnPointList;
  
     // array of which spawn points are currently available for spawning at
     private ArrayList spawnIndexAvailableList;
  
     // variable to hold the total number of spawn points, saves having to recalculate
     private int numberOfSpawnPoints;
 
     void Awake()
     {
         // retrieve GameObjects tagged as 'SpawnPoint' within the 'PickupSpawnPoints' GameObject which this script is a Component of
         spawnPointList = GameObject.FindGameObjectsWithTag("SpawnPoint");
         
         // retreive number of spawn points
         numberOfSpawnPoints = spawnPointList.length;
         
         // make sure number of pickups doesn't exceed number of spawn points
         if (numberOfPickups > numberOfSpawnPoints) numberOfPickups = numberOfSpawnPoints;
         
         // make all spawn points available by setting each index to true
         for (int i = 0;  i < numberOfSpawnPoints; i++) 
             {
                 spawnIndexAvailableList[i] = true;
             }
         // spawn X amount of pickups according to numberOfPickups
         for (int j = 0;  j < numberOfPickups; j++)  
             {
                 SpawnPickup();
             }
     }
     
     void SpawnPickup()
     {
         // generate a random integer to use as the index to select a spawn point from the list
         int randomSpawnIndex = Random.Range(0, numberOfSpawnPoints);
         
         // while the selected spawn index is unavailable regenerate another one
         while (!spawnIndexAvailableList[randomSpawnIndex])
             {
                 randomSpawnIndex = Random.Range(0, numberOfSpawnPoints);
             }
         // retrieve the position and rotation of the pickups spawn point
         Vector3 spawnedPickupPosition = spawnPointList[randomSpawnIndex].transform.position;
         Quaternion spawnedPickupRotation = spawnPointList[randomSpawnIndex].transform.rotation;
         
         // instantiate (create) the pickup prefab with the above position and rotation
         spawnedPickup = Instantiate(pickupPrefab, spawnedPickupPosition, spawnedPickupRotation)as GameObject;
         
         // set the spawned pickup as a child of the 'PickupSpawnPoints' gameobject that this script is a Component of
         // this is so we can use SendMessageUpwards within scripts attached to the pickupPrefab to call functions within this script
         spawnedPickup.transform.parent = spawnPointList[randomSpawnIndex].transform;
         
         // set the name of the pickup as its index
         spawnedPickup.name = randomSpawnIndex.ToString();
         
         // make the spawn index unavailable to prevent another pickup being spawned in this position
         spawnIndexAvailableList[randomSpawnIndex] = false;
 
     }
 
 }

This is what I have up to this point in the tutorial. Hopefully once I get the arrays fixed I can get the rest of the tutorial done tonight. Any suggestions?