C# 将文件加载到ftp站点时出现错误：系统：远程服务器返回错误：125数据连接已打开；转移起动

我正试图上传一些txt文件到ftp网站如下

FtpWebRequest request = (FtpWebRequest)WebRequest.Create("FTP PATH");
request.Method = WebRequestMethods.Ftp.UploadFile;
request.Credentials = new System.Net.NetworkCredential(username, password);
request.EnableSsl = true;
X509Certificate cert = X509Certificate.CreateFromCertFile(certificate path);
X509CertificateCollection certCollection = new X509CertificateCollection();
certCollection.Add(cert);
request.ClientCertificates = certCollection;
StreamReader sourceStream = new StreamReader("localfile path to upload");
 byte[] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd());
 sourceStream.Close();
 request.ContentLength = fileContents.Length;
 Stream requestStream = request.GetRequestStream();
 requestStream.Write(fileContents, 0, fileContents.Length);
 requestStream.Close();
FtpWebResponse response = (FtpWebResponse)request.GetResponse();
response.StatusDescription);
 writelog("response:.."+response.StatusDescription);
 response.Close();

有时上传文件，有时我会遇到一个错误。 请查看下面的日志

成功记录

4/12/2017 10:43:16 AM:Uploading file to ftp
4/12/2017 10:43:21 AM:response:..226 Closing data connection, Binary transfer complete.

4/12/2017 10:43:21 AM:end Uploading file to ftp

故障日志

4/12/2017 10:43:16 AM:Uploading file to ftp
4/12/2017 10:43:21 AM:response:..226 Closing data connection, Binary transfer complete.

4/12/2017 10:43:21 AM:end Uploading file to ftp

2017年4月12日上午10:43:22：将文件上载到ftp
2017年4月12日上午10:43:23： 系统：远程服务器返回错误：125数据连接 已经开放；换乘开始

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我无法确定问题所在，请帮助

显示日志文件-+独立FTP客户端是否存在类似问题？失败或成功的文件有什么共同点吗？@BugFinder所有文件都只包含一些文本