代码如下：

        string ftpdir = FTPAddress;
        string temofolder = Application.StartupPath + "\\Temp\\";
        Parallel.ForEach(downloaduris,(downloaduri, state) =>
        {
            FileInfo fileInfo = new FileInfo(temofolder + downloaduri);
            string sDir = fileInfo.DirectoryName;
            if (!Directory.Exists(sDir))//文件夹不存在则创建
            {
                Directory.CreateDirectory(sDir);
            }
            try
            {
                FtpWebRequest reqFTP = (FtpWebRequest)WebRequest.Create(ftpdir + "//" + downloaduri);
                reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
                FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();
                FileStream outputStream = new FileStream(temofolder + downloaduri, FileMode.Create);
                int bufferSize = 2048;
                byte[] buffer = new byte[bufferSize];
                Stream ftpStream = response.GetResponseStream();
                int readCount = ftpStream.Read(buffer, 0, bufferSize);
                while (readCount > 0)
                {
                    outputStream.Write(buffer, 0, readCount);
                    readCount = ftpStream.Read(buffer, 0, bufferSize);
                }
                ftpStream.Flush();
                ftpStream.Close();
                outputStream.Flush();
                outputStream.Close();
                response.Close();
                reqFTP.Abort();
            }
            catch (WebException webex)
            {   //FTP上不存在该文件
                state.Stop();
            }
        });

downloaduris 里面是200多张图片或TXT文本的相对路径。
在下载之前Temp文件夹是清过的。
在 FileStream outputStream = new FileStream(temofolder + downloaduri, FileMode.Create);
这句话经常报这样的错：
System.IO.IOException
"D:\PYProject\UpFile\Temp\Dog20180202\dog11.png"正由另一个进程使用，因此该进程无法访问此文件。

有没有大神解答一下