FTPS error 550 with FTPwebrequest

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Net;
namespace ConsoleApplication1
{
    class Class1
    {
        public static void Main(string[] args)
        {
            Stream requestStream = null;
            FileStream fileStream = null;
            FtpWebResponse uploadResponse = null;
            try
            {
                Uri uploadUrl = new Uri("ftp://blaabll.blabala.com/folder/");
                string fileName = "c:\\sangeetha.xlsx";
                FtpWebRequest uploadRequest =
                 (FtpWebRequest)WebRequest.Create(uploadUrl + @"/" + fileName);
                uploadRequest.Method = WebRequestMethods.Ftp.UploadFile              //Since the FTP you are downloading to is secure, send
                //in user name and password to be able upload the file
                ICredentials credentials = new NetworkCredential(user, password);
                uploadRequest.Credentials = credentials;
                //UploadFile is not supported through an Http proxy
                //so we disable the proxy for this request.
                uploadRequest.Proxy = null;
                //uploadRequest.UsePassive = false; <--found from another forum and did not make a difference
           <b>      requestStream = uploadRequest.GetRequestStream()</b> 
                fileStream = File.Open(fileName, FileMode.Open);
                byte[] buffer = new byte[1024];
                int bytesRead;
                while (true)
                {
                    bytesRead = fileStream.Read(buffer, 0, buffer.Length);
                    if (bytesRead == 0)
                        break;
                    requestStream.Write(buffer, 0, bytesRead);
                }
                //The request stream must be closed before getting
                //the response.
                requestStream.Close();
                uploadResponse =
                  (FtpWebResponse)uploadRequest.GetResponse();
            }
            catch (UriFormatException ex)
            {
             //   ErrorsHappened.Items.Add("Error: " + ex.Message);
            }
            catch (IOException ex)
            {
              // ErrorsHappened.Items.Add("Error: " + ex.Message);
            }
            catch (WebException ex)
            {
                //ErrorsHappened.Items.Add("Error: " + ex.Message);
            }
            finally
            {
                if (uploadResponse != null)
                    uploadResponse.Close();
                if (fileStream != null)
                    fileStream.Close();
                if (requestStream != null)
                    requestStream.Close();
            }
        }
    }
}