UserID already joined the specified game. (JoinMode = 0, Return Code: 32747)

Hello everyone!
I got an error when i try to join a room and in that room, already have a player whose name is the same as mine.
Operation failed: OperationResponse 226: ReturnCode: 32746 (Join failed: UserId 'thiten2' already joined the specified game (JoinMode=0).). Parameters: {} Server: GameServer
UnityEngine.Debug:LogError(Object)
NetworkingPeer:OnOperationResponse(OperationResponse) (at Assets/Photon Unity Networking/Plugins/PhotonNetwork/NetworkingPeer.cs:1669)
ExitGames.Client.Photon.PeerBase:DeserializeMessageAndCallback(StreamBuffer)
ExitGames.Client.Photon.EnetPeer:DispatchIncomingCommands()
ExitGames.Client.Photon.PhotonPeer:DispatchIncomingCommands()
PhotonHandler:Update() (at Assets/Photon Unity Networking/Plugins/PhotonNetwork/PhotonHandler.cs:161)"

In my code when i connect to server, i just use:
 PhotonNetwork.ConnectUsingSettings("1.0.3" + "");
 PhotonNetwork.playerName =  GUILayout.TextField(PhotonNetwork.playerName);

So it mean that i didn't given a userID, but when i display photonnetwork.player.UserID, i got the same result as photonnetwork.player.NickName. So I think the reason was here, the photon was automatically assigned userID = NickName. But when i changed UserID to a new random string, i still got this problem :'(.

What's happened? Can someone help me pls (?