ftp webrequest with SSL error

i am not sure what i am doing wrong. any help would be appreciated. maybe SSL is not configured properly on my server?

error:
The remote server returned an error: (500) Syntax error, command unrecognized.

Code:

---

Me.ListBoxFTPFiles.Items.Clear()

Dim fwr As System.Net.FtpWebRequest = System.Net.FtpWebRequest.Create("ftp://ftp.site.com")

fwr.UsePassive = False
fwr.UseBinary = True
fwr.EnableSsl = True

fwr.Credentials = New System.Net.NetworkCredential("username", "password")
fwr.Method = System.Net.WebRequestMethods.Ftp.ListDirectory

Dim sr As New System.IO.StreamReader(fwr.GetResponse().GetResponseStream()) 'this is the error
Dim str As String = sr.ReadLine()

While Not str Is Nothing
    Me.ListBoxFTPFiles.Items.Add(str)
    str = sr.ReadLine()
End While

sr.Close()
sr = Nothing
fwr = Nothing

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