Unity Multiplayer non-player object destroy

I am trying to create a 2D top down multiplayer game where the players move and pickup objects.

Below is the spawning of 6 pick-up objects on a random 2D position. This script is attached to a game object in the scene called PickupSpawner.

public class PickupGen : NetworkBehaviour {

    public GameObject pickup;

    // Use this for initialization
    public override void OnStartServer () {
        print ("In OnStartServer");
        float x, y;
        for (int i = 0; i < 6; i++) {
            x = Random.Range (-4.5f, 4.5f);
            y = Random.Range (-4.5f, 4.5f);
            Vector3 pos = new Vector3 (x, y,0);
            GameObject go = (GameObject) Instantiate (pickup, pos,Quaternion.identity);
            NetworkServer.Spawn (go);
        }
    }
}

The problem occurs when I try to destroy the objects after they are picked up. I am using the OnTriggerEnter2D with colliders as shown below. Note: All of this worked without network/multiplayer.

I have attempted to do this in many different ways. Below I am trying to use the [Command] attribute to tell the server to destroy the pickup object. I don't think I fully understand whats going on as I get this error after running and trying to pickup(destroy) a pickup object as the client(Note: It works fine as server(host)):

Found no behaviour for incoming [Command:InvokeCmdCmdDestroyPickup] on Player(Clone) (UnityEngine.GameObject), the server and client should have the same NetworkBehaviour instances [netId=9]. UnityEngine.Networking.NetworkIdentity:UNetStaticUpdate()

I have no idea what this means and I didn't get much insight from searching google for it. Any explanation would be appreciated. Thanks.

    void OnTriggerEnter2D(Collider2D other) {
        print ("In OnTrigger");

        GameObject otherGO = other.gameObject;
        if (otherGO.CompareTag ("Pickup")) {
//          otherGO.SetActive (false);
//          Destroy (otherGO);
            CmdDestroyPickup (otherGO);
        }
    }

    [Command]
    public void CmdDestroyPickup(GameObject go){
        NetworkServer.Destroy (go);
    }