Network.Spawned objects won't show on new client

Hello, I've just recently got the Network.Spawn to actually spawn what I need on all Clients before I realized that when spawning an objects on all connected clients(through [Command]), it still won't show to a newly connected one. I do register prefabs on Start() of the Player GameObject and I get no problems when spawning on connected players, when a player joins instead, he gets this until the object is destroyed:

Did not find target for sync message for 4 UnityEngine.Networking.NetworkIdentity:UNetStaticUpdate()

What am I doing wrong?

Command:

     [Command]
     public void CmdSpawnThrowable(Vector3 fwd, Vector3 pos, string name)
     {
         GameObject item = Instantiate(Resources.Load(name), pos, Quaternion.identity) as GameObject;
         if (item.GetComponent<Collider>())
             item.GetComponent<Collider>().isTrigger = false;
         else
             item.AddComponent<Collider>();
         Rigidbody body = item.GetComponent<Rigidbody>();
         if (!body)
             body = item.AddComponent<Rigidbody>();
         body.AddForce(fwd * 600 * body.mass);
         NetworkServer.Spawn(item);
     }

Call when Player presses a button:

                 if (isLocalPlayer)
                     CmdSpawnThrowable(player.transform.forward, player.righthand.transform.position, name);