The handshake failed due to an unexpected packet format

Most likely your FTP server requires explicit SSL. So first try to connect without SSL:

// C#

client.Connect("ftp.example.org");

' VB.NET

client.Connect("ftp.example.org")

Then, before logging-in, start explicit SSL negotiation:

// C#

client.AuthSSL();

' VB.NET

client.AuthSSL()

Now, your connection is secured.

Remember that you can ignore SSL certificate errors using ServerCertificateValidate event:

// C# version

using (Ftp client = new Ftp())
{
    // Use this line to validate self-signed certificates:
    client.ServerCertificateValidate += ValidateCertificate;

    client.Connect("ftp.example.org");
    client.AuthSSL();
    client.Login("username", "password");

    foreach (FtpItem item in client.GetList())
    {
        if (item.IsFolder == true)
            Console.WriteLine("[{0}]", item.Name);
        else
            Console.WriteLine("{0}", item.Name);
    }
    client.Close();
}

private static void ValidateCertificate(
    object sender,
    ServerCertificateValidateEventArgs e)
{
    const SslPolicyErrors ignoredErrors =
        SslPolicyErrors.RemoteCertificateChainErrors |
        SslPolicyErrors.RemoteCertificateNameMismatch;

    if ((e.SslPolicyErrors & ~ignoredErrors) == SslPolicyErrors.None)
    {
        e.IsValid = true;
        return;
    }
    e.IsValid = false;
}

' VB.NET version

Using client As New Ftp()
    ' Use this line to validate self-signed certificates:
    AddHandler client.ServerCertificateValidate, AddressOf ValidateCerificate

    client.Connect("ftp.example.org")
    client.AuthSSL()
    client.Login("username", "password")

    For Each item As FtpItem In client.GetList()
        If item.IsFolder = True Then
            Console.WriteLine("[{0}]", item.Name)
        Else
            Console.WriteLine("{0}", item.Name)
        End If
    Next
    client.Close()
End Using

Private Sub ValidateCerificate( _
    ByVal sender As Object, _
    ByVal e As ServerCertificateValidateEventArgs)

    Const ignoredErrors As SslPolicyErrors = _
        SslPolicyErrors.RemoteCertificateChainErrors Or _
        SslPolicyErrors.RemoteCertificateNameMismatch

    If (e.SslPolicyErrors And Not ignoredErrors) = SslPolicyErrors.None Then
        e.IsValid = True
        Return
    End If
    e.IsValid = False
End Sub

You can download Ftp.dll FTP/FTPS client for .NET here.

Tags: C# FTP FTP component FTPS VB.NET