Project console :
You have been disconnected. Reason: Could not get authentication key from master server

Server console displays :
Could not advertise to master server:
Lidgren.Network.NetException: Unconnected messages too long! Must be shorter than NetConfiguration.MaximumTransmissionUnit (currently 1408)
   à Lidgren.Network.NetPeer.SendUnconnectedMessage(NetOutgoingMessage msg, IPEndPoint recipient)
   à CraftStudioServer.Server.Advertise()

craftstudioserver.exe is authorised in the firewall
The client gets succeffully online and I can connect to other remote projects

What can I do ?