Download from FTP Server Error: 550 The system cannot find the file specified

Hi Sir ,

I am downloading the file from FTP Server but i am facing some error. I have uploading the file to FTP successfully but i have downloaded the file but still facing some error kindly help me.

Error - System.Exception: '550 The system cannot find the file specified. 

string fileName = "139459_AE_IE_SC Contract_V32.pdf";
string ftp = "ftp://16.12.133.33/";
string ftpFolder = "UploadToDMS/139459";

try
{
    //Create FTP Request.
    FtpWebRequest request = (FtpWebRequest)WebRequest.Create(ftp + ftpFolder + fileName);
    request.Method = WebRequestMethods.Ftp.DownloadFile;

    //Enter FTP Server credentials.
    request.Credentials = new NetworkCredential(userName, password);
    //request.Credentials = new NetworkCredential("Username", "Password");
    request.UsePassive = true;
    request.UseBinary = true;
    request.EnableSsl = false;

    //Fetch the Response and read it into a MemoryStream object.
    FtpWebResponse response = (FtpWebResponse)request.GetResponse();
    using (MemoryStream stream = new MemoryStream())
    {
        //Download the File.
        response.GetResponseStream().CopyTo(stream);
        Response.AddHeader("content-disposition", "attachment;filename=" + fileName);
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        Response.BinaryWrite(stream.ToArray());
        Response.End();
    }
}
catch (WebException ex)
{
    //String status = ((FtpWebResponse)ex.Response).StatusDescription;
    throw new Exception((ex.Response as FtpWebResponse).StatusDescription);
}
//End FTP