My gRPC-Test Project just work on localhost

i have the following problem.

I created a gRpc Server(Console App .Net 4.7.2 - i cant do Net Core on Server Side because of Crystal Reports :() and a Client(WPF App .Net Core 3.1) and i can run it as long as Server and Client are on my machine (Windows 10). As far es i take my Server to another machine (windows Server 2016), it does not work anymore.

this is the RPC Exception:

Status(StatusCode="Unavailable", Detail="failed to connect to all addresses", DebugException="Grpc.Core.Internal.CoreErrorDetailException: {"created":"@1595508082.170000000","description":"Failed to pick subchannel","file":"T:\src\github\grpc\workspace_csharp_ext_windows_x64\src\core\ext\filters\client_channel\client_channel.cc","file_line":3948,"referenced_errors":[{"created":"@1595508082.170000000","description":"failed to connect to all addresses","file":"T:\src\github\grpc\workspace_csharp_ext_windows_x64\src\core\ext\filters\client_channel\lb_policy\pick_first\pick_first.cc","file_line":394,"grpc_status":14}]}")

i tried all variations. Here is my lastcode that works on localhost:

Server:

static void Main(string[] args)
    {
        var cacert = File.ReadAllText(@"root.crt");
        var servercert = File.ReadAllText(@"server.crt");
        var serverkey = File.ReadAllText(@"server.key");
        var keypair = new KeyCertificatePair(servercert, serverkey);
        var sslCredentials = new SslServerCredentials(new List<KeyCertificatePair>() { keypair }, cacert, false);

        // Build a server
        var server = new Server
        {
            Services = { ReportService.BindService(new KKarteReportService()) },
            Ports = { new ServerPort(Host, Port, sslCredentials) }
        };


        // Start server
        server.Start();

        Console.WriteLine("KKarteReport Server listening on port " + Port);
        Console.WriteLine("Press any key to stop the server...");
        Console.ReadKey();

        server.ShutdownAsync().Wait();
    }

Client

var cacert = File.ReadAllText(@"root.crt");
var clientcert = File.ReadAllText(@"client.crt");
var clientkey = File.ReadAllText(@"client.key");
var ssl = new SslCredentials(cacert, new KeyCertificatePair(clientcert, clientkey));
           
 var options = new List<ChannelOption> { new ChannelOption(ChannelOptions.SslTargetNameOverride, "MyServerHost") }; 
 var channel = new Channel("12.20.18.11", 5001, ssl, options);
 //var channel = new Channel("localhost", 5001, ssl, options);
 //var channel = new Channel(url, ChannelCredentials.Insecure);
 var client = new ReportService.ReportServiceClient(channel);

  using var streamingCall = client.CreateAusschreibung(request);

  await using var ms = new MemoryStream();

  while (await streamingCall.ResponseStream.MoveNext())
  {
        ms.Write(streamingCall.ResponseStream.Current.FileChunk.ToByteArray());
  }

What do i miss?