Network Instantiate PlayerPrefab Problem

I have a problem with instantiating my Prefabs on different Clients.

When the first client is connected to server he can move the way he should.
But when the second is connected to server there are some problems:

On the first client appears a copy of the first player so I do move 2 Characters (one of them collides with the player of client 2 and the other not. The second player moves the correct way like on the second Client.

Does anyone know how to solve this problem?

Here is my Code:

using uLink;

using UnityEngine;

public class InstantiateScript : uLink.MonoBehaviour
    public GameObject PlayerPrefab;
    private GameObject playerAvatar;
    public static GUIText lifePointsAvatar;
    public static bool loggedIn;
    private int level;

    void OnLevelWasLoaded(int level) 
                networkView.RPC("Instantiate", uLink.RPCMode.AllBuffered, "test"); 

    public void uLink_OnPlayerDisconnected(uLink.NetworkPlayer player)
        // Removing player from network and scene
        uLink.Network.RemoveRPCs(player, 0);

    void Instantiate(string test)
            playerAvatar = uLink.Network.Instantiate(PlayerPrefab, transform.position, transform.rotation, 0);
            Debug.Log("Network aware game object is now created on client" + playerAvatar);
            loggedIn = true;

For almost every script I create that will be on network.instantiate i use

if (!networkView.isMine)
     this.enabled = false;

You don’t need to RPC a Network.Instantiate.
When you use Network.Instantiate you are already doing a buffered RPC.
So, if you call it on RPC you are kind of doing the same thing twice, thus two instances.
I had a similar problem myself.