Argument out of Range

I am having a little trouble fixing this small problem in my code. Firstly the game is a card game, and my trouble occurs when I go to deal a card from the deck. I have checked if the deck actually contains information, which is it does. So on first start the game.cs initialize the different decks and adds the cards into each. Again I have checked if the information is being passed which it is.

Once the start function has finished the game state is changed to initial which then runs a function for setting up the player's and enemy's hands.

 Game.cs
 
 void InitialSetUp()
     {
         for(int i = 0; i<5;i++)
         {
             AddToEnemyHand();
             AddToPlayerHand();
         }
         FlipCoin();
         m_state = GameState.Begin;
     }
 
     void AddToPlayerHand()
     {
         List<System.Object> c1 = new List<System.Object>();
         playerDeck.Deal (c1);

This seems to be working fine up until it gets to the last part I have included in the code. Once it gets to playerDeck.Deal(c1) and calls the deal function I get the ArgumentOutOfRange error.

     public System.Object Deal(List<System.Object> returnCard)
     {
         returnCard.Add(deck[0]);
         deck.RemoveAt(0);
         return returnCard;
     }

A deck is a list of cards, and the reason it is currently System.Object is due to the fact that different types of cards have different classes, i.e. solider class, active class, magic class, etc. I plan on changing this. Anyway I haven't been able to figure out why I am getting this error.

Some help or a fresh set of eyes would be extremely appreciated.