Created Unassigned: SshOperationTimeoutException when forwarding local port [2758]

I am getting following exception while forwarding local port:

Renci.SshNet.Common.SshOperationTimeoutException: Session operation has timed out

Port forwarding starts, I am able to rsync through SSH tunnel, but at some point the exception I mentioned is thrown (but not always).

Here is the code:
```
using (SshClient sshClient = new SshClient(serverAddress, serverPort, "test_rsync", key))
{
try
{
sshClient.Connect();
using (ForwardedPortLocal forwardedPort = new ForwardedPortLocal("127.0.0.1", 873, "127.0.0.1", 873))
{
sshClient.AddForwardedPort(forwardedPort);
forwardedPort.Exception += delegate (object sender, ExceptionEventArgs ea)
{
MessageBox.Show(ea.Exception.ToString(), "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
};
forwardedPort.Start();
runBackup();
}
} catch (Exception ex)
{
MessageBox.Show(ex.ToString(), "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
}

```

Application is builded against .NET 4 Client profile. Any ideas what might be the cause?