(Photon) Why does LoadBalancingPeer not work?

When importing a FPS project I have got these error:

Assets\Photon\PhotonRealtime\Code\ConnectionHandler.cs(358,70): error CS1061: ‘LoadBalancingPeer’ does not contain a definition for ‘SocketErrorCode’ and no accessible extension method ‘SocketErrorCode’ accepting a first argument of type ‘LoadBalancingPeer’ could be found (are you missing a using directive or an assembly reference?)

I will be sp thankful if you help me out

Did you manage to solve this? I am getting the same error