Return a Hashtable. Warning: Implicit downcast from Object to String.

Here's the simplified version of the code:

 var h:Hashtable = new Hashtable();
 h = returnHash();
 
 function returnHash():Hashtable{
     var h2:Hashtable = new Hashtable();
     h2.Add("key",1);
     return h2;
 }

When I do this then the game just freeze at that point. Any help or work round would be appreciate