The remote server returned an error: (550) File unavailable

Question

hi all,
        i am using c# code to upload large files using FPT protocole but it gives Erorr while reading this line code:

       System.IO.Stream _Stream = _FtpWebRequest.GetRequestStream();
Error is

    The remote server returned an error: (550) File unavailable (e.g., file not found, no access).Error number is 017

my whole code is

            System.IO.FileInfo _FileInfo = new System.IO.FileInfo(_FileName);

            // Create FtpWebRequest object from the Uri provided

            System.Net.FtpWebRequest _FtpWebRequest = (System.Net.FtpWebRequest)System.Net.FtpWebRequest.Create(new Uri(_UploadPath));

            // Provide the WebPermission Credintials

            _FtpWebRequest.Credentials = new System.Net.NetworkCredential(_FTPUser, _FTPPass);

            // By default KeepAlive is true, where the control connection is not closed

            // after a command is executed.

            _FtpWebRequest.KeepAlive = false;

            // set timeout for 20 seconds

            _FtpWebRequest.Timeout = 20000;

            // Specify the command to be executed.

            _FtpWebRequest.Method = System.Net.WebRequestMethods.Ftp.UploadFile;

            // Specify the data transfer type.

            _FtpWebRequest.UseBinary = true;

            // Notify the server about the size of the uploaded file

            _FtpWebRequest.ContentLength = _FileInfo.Length;

            // The buffer size is set to 2kb

            int buffLength = 2048;

            byte[] buff = new byte[buffLength];

            // Opens a file stream (System.IO.FileStream) to read the file to be uploaded

            System.IO.FileStream _FileStream = _FileInfo.OpenRead();

            try

            {

                // Stream to which the file to be upload is written

                System.IO.Stream _Stream = _FtpWebRequest.GetRequestStream();

                // Read from the file stream 2kb at a time

                int contentLen = _FileStream.Read(buff, 0, buffLength);

                // Till Stream content ends

                while (contentLen != 0)

                {

                    // Write Content from the file stream to the FTP Upload Stream

                    _Stream.Write(buff, 0, contentLen);

                    contentLen = _FileStream.Read(buff, 0, buffLength);

                }

                // Close the file stream and the Request Stream

                _Stream.Close();

                _Stream.Dispose();

                _FileStream.Close();

                _FileStream.Dispose();

            }

catch (Exception ex)

            {

                Console.WriteLine(ex.Message,"Upload Error");

            }
plz help