title: Unity can not cast GameObject to my object
body: <p>I am writing a simple board game using unity.
  I need to set a property of my object (Player), although I have a reference to it as a GameObject. I need to cast, but cant. 
  Here is what i have tried</p>
  
  <pre><code>public GameObject PlayerPrefab;
  
  private GameObject player;
  
  // Use this for initialization
  void Start () {
      if (!isLocalPlayer)
      {
          return;
      }
      Debug.Log("Spawning.");
      CmdSpawn();
  }
  
  
  [Command]
  void CmdSpawn()
  {
      player = Instantiate(PlayerPrefab);
      ((Player)player).parentNetId = this.netId;
      NetworkServer.SpawnWithClientAuthority(player, connectionToClient);
  }
  </code></pre>
  
  <p>I have the following error:
  "Assets/Scripts/PlayerConnectionObject.cs(27,18): error CS0030: Cannot convert type <code>UnityEngine.GameObject' to</code>Player'"</p>