FTP Error coming when downloading file before it working and after installation new windows it not working

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C#2.0

C#

I using this code for download file from FTP. SO I install new windows so the same code not working and give the following error.

The remote server returned an error: (550) File unavailable (e.g., file not found, no access)

public void FileDownload(string Servername, string username, string Pwd, string Filename)
        {
            try
            {             

                WebProxy prox = new WebProxy();
                prox.UseDefaultCredentials = true;
                WebClient request = new WebClient();              
                request.Credentials = new NetworkCredential(username, Pwd);
                request.Proxy = prox;               
                byte[] fileData = request.DownloadData(Servername + "/" + "/fashionretailkz/SHIPMENTFILES/IN/" + Filename);
                DirectoryInfo di = new DirectoryInfo(txtdrive.Text +@"\DownloadfilefrmTAP");
                if (di.Exists == false)
                    di.Create();

              FileStream file = File.Create(txtdrive.Text +@"\\DownloadfilefrmTAP\" + Filename);
                 file.Write(fileData, 0, fileData.Length);
                              file.Close();
            }
            catch (SystemException ex)
            {
                Logs.MakeLog(Application.StartupPath.ToString(), ex.ToString());
            }
            
        }

So please guide me what is the problem..


[edit]Code block added - OriginalGriff[/edit]