Hey somebody now how to fix this error?

[Error] System.IO.IOException: Unable to read data from the transport connection: Eine vorhandene Verbindung wurde vom Remotehost geschlossen.
. ---> System.Net.Sockets.SocketException: Eine vorhandene Verbindung wurde vom Remotehost geschlossen.

  at System.Net.Sockets.Socket.EndReceive (System.IAsyncResult asyncResult) [0x00012] in <ef151b6abb5d474cb2c1cb8906a8b5a4>:0 
  at System.Net.Sockets.NetworkStream.EndRead (System.IAsyncResult asyncResult) [0x00057] in <ef151b6abb5d474cb2c1cb8906a8b5a4>:0 
   --- End of inner exception stack trace ---
  at System.Net.Sockets.NetworkStream.EndRead (System.IAsyncResult asyncResult) [0x0009b] in <ef151b6abb5d474cb2c1cb8906a8b5a4>:0 
  at Fleck.WebSocketConnection+<>c.<Receive>b__63_0 (System.IAsyncResult result) [0x00017] in <ab99eefdd17e4a4e88de8ba5c29af877>:0