Error while copying large files(300 MB more) using FTP

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C#

I got Error while copying large size file(300MB or more) from one server to another using FTP
here is my code

public void FTPUpload(string p_FilePath, string p_FTPServer, string p_Username, string p_Password)
        {
            try
            {
                //Reading file into a byte array
                byte[] file = null;
                file = System.IO.File.ReadAllBytes(p_FilePath);

                //Request
                System.Net.FtpWebRequest req = null;
                req = (System.Net.FtpWebRequest)System.Net.WebRequest.Create(p_FTPServer);
                req.KeepAlive = false;
                req.UsePassive = true;
                req.UseBinary = true;
                req.Proxy = null;

                //timeout set to 40 minute need to change
                req.Timeout = 2400000;
                req.ReadWriteTimeout = 2400000;

                //Credentials
                System.Net.NetworkCredential credentials = new System.Net.NetworkCredential(p_Username, p_Password);
                req.Credentials = credentials;

                //Request Method
                req.Method = System.Net.WebRequestMethods.Ftp.UploadFile;

                //uploading file onto FTP server
                System.IO.Stream stream = null;

                stream = req.GetRequestStream();
                stream.Write(file, 0, file.Length);
                stream.Close();

            }
            catch (Exception ex)
            {
                Util.WriteToErrorLogFile(ex, "Error:017", "From FTP File laod of Service");
            }
        }

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