Collections don't work!

Hi guys.

This one is driving me nuts! The only collection I can use is the regular Array. List, ArrayList etc. simply don't work!

I get a "the name .... does not exist in the current context."

I have absolutely no idea what the problem is.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class ScoreMgr : MonoBehaviour {
 
     public ArrayList myList;
         public List<int> myList2;
 
 }