Unable to connect to AIX(Unix) box with SSH.NET Library - Error : Value cannot be null

I am trying to connect to an AIX box and execute some commands using SSH.NET library. The following is the code snipplet

KeyboardInteractiveAuthenticationMethod kauth = new KeyboardInteractiveAuthenticationMethod(username);
PasswordAuthenticationMethod pauth = new PasswordAuthenticationMethod(username, password);

ConnectionInfo connectionInfo = new(ConnectionInfo(servername, 22, username, pauth,kauth);
SshClient sshClient = new SshClient(connectionInfo);
sshClient.Connect();
SshCommand sshCommand = sshClient.RunCommand("mpstat");
Console.WriteLine(sshCommand.Result);
Console.ReadKey();

I get the following exception message when I try to connect at the line sshClient.Connect()

{"Value cannot be null.\r\nParameter name: data"}

The stack trace is

   at Renci.SshNet.KeyboardInteractiveAuthenticationMethod.Authenticate(Session session)
   at Renci.SshNet.ConnectionInfo.Authenticate(Session session)
   at Renci.SshNet.Session.Connect()
   at Renci.SshNet.BaseClient.Connect()

I am confident that the credentials I pass are valid since I am able to log-in using the PuTTY client with the same credentials. Any ideas?