I have found the solution self. My fail was in the PortForward command. I have used only this parameters:
port = client.AddForwardedPort<Renci.SshNet.ForwardedPortLocal>((uint)localport, destinationHost, (uint)remoteport);
I think as local server address take the library the name "localhost". This works with RDP but not with the SQL Server connection.
I have changed the line to:
port = client.AddForwardedPort<Renci.SshNet.ForwardedPortLocal>(sourcehost, (uint)localport, destinationHost, (uint)remoteport);
sourcehost is "127.0.0.1"
This works with the SQL Management Studio and with my program that connect to the SQL server. The RDP works with this settings too....
Thanks for the quick anwser...
This library is very goood... Thanks.... Can you say when the compression option for the normal ssh connection is