Network View - Player is blinking, and visible only partially during movement.

I've got a problem. I made my game multiplayer, but the player (box) is blinking while moving. I'm from poland, so there can be some of polish words between quotes.

Here is my network code:

 var playerPrefab:GameObject;
 var spawnObject:Transform;
 
 var nameofGame:String = "MyFirstMultiplayer";
 
 private var refreshing:boolean;
 private var hostData:HostData[];
 
 private var btnX:float;
 private var btnY:float;
 private var btnW:float;
 private var btnH:float;
 
 function Start(){
     btnX = Screen.width * 0.2;
     btnY = Screen.height * 0.2;
     btnW = Screen.width * 0.1;
     btnH = Screen.width * 0.03;
 }
 
 function startServer(){
     Network.InitializeServer(32, 25001, !Network.HavePublicAddress);
     MasterServer.RegisterHost(nameofGame, "FirstMulti", "Multiplayer");
 }
 
 function refreshHostList(){
  MasterServer.RequestHostList(nameofGame);
  refreshing = true;
  Debug.Log(MasterServer.PollHostList().Length);
 }
 
 function Update(){
     if(refreshing){
         if(MasterServer.PollHostList().Length > 0){
             refresh = false;
             Debug.Log(MasterServer.PollHostList().Length);
             hostData = MasterServer.PollHostList();
         }
     }
 }
 
 function spawnPlayer(){
     Network.Instantiate(playerPrefab, spawnObject.position, Quaternion.identity, 0);
 }
 
 
 //Wiadomości
 function OnServerInitialized(){
     Debug.Log("Serwer uruchomiony!");
     spawnPlayer();
 }
 
 function OnConnectedToServer(){
     spawnPlayer();
 }
 
 function OnMasterServerEvent(mse:MasterServerEvent){
     if(mse == MasterServerEvent.RegistrationSucceeded){
         Debug.Log("Zarejestrowano serwer!");
     }
 }
 
 //GUI
 function OnGUI(){
     if(!Network.isClient && !Network.isServer){
     if(GUI.Button(Rect(btnX, btnY, btnW, btnH), "Utwórz serwer")){
         Debug.Log("Uruchamianie serwera...");
         startServer();
     }
     
     if(GUI.Button(Rect(btnX, btnY * 1.2 + btnH, btnW, btnH), "Odśwież listę serwerów")){
         Debug.Log("Odświeżanie...");
         refreshHostList();
     }
     
     if(hostData){
         for(var i:int = 0; i<hostData.length; i++){
             if(GUI.Button(Rect(btnX*1.5 + btnW, btnY*1.2 + (btnH * i), btnW*3, btnH), hostData[i].gameName)){
                 Network.Connect(hostData[i]);
             }
         }
     }
     }
 }