How come I can't change a collections key value after the add. It would seem this would be a key feature of the collection object.

  lo_collection = NEWOBJECT('Collection')
  lo_Collection.Add('item','key')
  ? lo_collection.Item('key') && Prints 'item'
  lo_collection.Item('key') = "Newitem" 

this last line gives error message "Function argument value, type, or count is invalid." Is there a different way to change the collection key's value?