Adding new properties like PhotonNetwork.Nickname

Hello,

For my game, it's nesesary to add new properties like nickname as team or others.
I've add in Photon code and it works well, but I think is giving me an error when player disconnects from the server.

The error is that:
InvalidOperationException: Collection was modified; enumeration operation may not execute.
System.ThrowHelper.ThrowInvalidOperationException (System.ExceptionResource resource) (at <eae584ce26bc40229c1b1aa476bfa589>:0)
System.Collections.Generic.List`1+Enumerator[T].MoveNextRare () (at <eae584ce26bc40229c1b1aa476bfa589>:0)
System.Collections.Generic.List`1+Enumerator[T].MoveNext () (at <eae584ce26bc40229c1b1aa476bfa589>:0)
Photon.Realtime.InRoomCallbacksContainer.OnPlayerLeftRoom (Photon.Realtime.Player otherPlayer) (at Assets/Photon/PhotonRealtime/Code/LoadBalancingClient.cs:4362)
Photon.Realtime.LoadBalancingClient.OnEvent (ExitGames.Client.Photon.EventData photonEvent) (at Assets/Photon/PhotonRealtime/Code/LoadBalancingClient.cs:3377)
ExitGames.Client.Photon.PeerBase.DeserializeMessageAndCallback (ExitGames.Client.Photon.StreamBuffer stream) (at <bc80793ed5ef411a8b132f02589b3549>:0)
ExitGames.Client.Photon.TPeer.DispatchIncomingCommands () (at <bc80793ed5ef411a8b132f02589b3549>:0)
ExitGames.Client.Photon.PhotonPeer.DispatchIncomingCommands () (at <bc80793ed5ef411a8b132f02589b3549>:0)
Photon.Pun.PhotonHandler.Dispatch () (at Assets/Photon/PhotonUnityNetworking/Code/PhotonHandler.cs:221)
Photon.Pun.PhotonHandler.FixedUpdate () (at Assets/Photon/PhotonUnityNetworking/Code/PhotonHandler.cs:147)

Could anyone tell me if the error is for doing that and what other choice I have to add new properties?

Thanks a lot!