FTP Problem

I seem to be having a problem with the FTPWebRequest. I get an error (see below code) when it executes the emboldened line. Any ideas?

Code:

---

Dim uploadRequest As FtpWebRequest = WebRequest.Create(uploadUrl)
uploadRequest.Method = WebRequestMethods.Ftp.UploadFile

If strUserName <> "" And strPassword <> "" Then
      uploadRequest.Credentials = New System.Net.NetworkCredential(strUserName, strPassword)
End If

uploadRequest.EnableSsl = blnSecure
uploadRequest.KeepAlive = True
uploadRequest.UsePassive = blnPassive
uploadRequest.Proxy = Nothing

RequestStream = uploadRequest.GetRequestStream()
fileStream = File.Open(fileName, FileMode.Open)

Dim buffer(1024) As Byte
Dim bytesRead As Integer
While True
        bytesRead = fileStream.Read(buffer, 0, buffer.Length)
        If bytesRead = 0 Then
            Exit While
        End If
        requestStream.Write(buffer, 0, bytesRead)
End While

' The request stream must be closed before getting the response.
requestStream.Close()

uploadResponse = uploadRequest.GetResponse()

---

"The server returned an address in response to the PASV command that is different than the address to which the FTP connection was made."

Ugh, never seen that one. Is this in a test-bed situation or live? Do you know your network route to the server? Are there anything like proxy servers, firewalls or anything else in between that could be passing you a different IP?

Is the server you're talking to on multiple IP addresses? Try accessing it by IP address rather than relying on DNS resolutions.

In answer to the above questions:

I am accessing it with an IP address rather than a DNS.
This is a testbed situation.
there are no proxy servers but there is a firewall.

I should have stated originally that this problem occurs when I am setting EnableSsl to True. I am also using passive mode (because I heard somewhere that you have to when using encryption). If I set EnableSsl to False, it uploads fine.

Further note, I have connected to the FTP server in question fine using a client tool (such as SmartFTP) with Explicit SSL and Passive mode switched on. The client tool works but the .NET code doesn't...