C#FTP上传上载

以下代码为FTP下载文件的代码，但下载下来的EXE文件在本地不能使用，请问是怎么回事？
 private void Download(string filePath, string fileName)
        {
            FtpWebRequest reqFTP;            string uri = "ftp://" + ftpServerIP + "/" + fileName;
            try
            {
                FileStream outputStream = new FileStream(filePath + "\\" + fileName, FileMode.Create);//本地文件路径及文件名                reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://" + ftpServerIP + "/" + "/home2/store/maintain/user.dmp"));//远程服务器文件路径                reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;                reqFTP.UseBinary = true;                reqFTP.Credentials = new NetworkCredential(ftpUserID, ftpPassword);                FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();                Stream ftpStream = response.GetResponseStream();                long cl = response.ContentLength;                int bufferSize = 2048;                int readCount;                byte[] buffer = new byte[bufferSize];                readCount = ftpStream.Read(buffer, 0, bufferSize);                while (readCount > 0)
                {
                    outputStream.Write(buffer, 0, readCount);                    readCount = ftpStream.Read(buffer, 0, bufferSize);
                }                ftpStream.Close();                outputStream.Close();                response.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }