【绝望求助】C# ftpwebrequest FTP上传失败

运行了很长一段时间一直没有问题，最近发现无法上传。
错误内容：
==========================================================
System.Net.WebException: 基础连接已经关闭: 接收时发生错误。
   在 System.Net.FtpWebRequest.SyncRequestCallback(Object obj)
   在 System.Net.FtpWebRequest.RequestCallback(Object obj)
   在 System.Net.CommandStream.Abort(Exception e)
   在 System.Net.FtpWebRequest.FinishRequestStage(RequestStage stage)
   在 System.Net.FtpWebRequest.GetRequestStream()
   在 FTPAPI.FTPAPI.transFileToFTP(String filePathp_source, String filePathp_aim, String uploadURIp, String userNamep, String passwordp, String EncryptKey, Exception& e)
==========================================================
测试发现只有特定一些路径上传时失败，在
Stream uploadStream = transFileRequest.GetRequestStream()
时抛异常。FTP服务器断日志发现登陆已完成，并且已经切换目录完成，之后就直接断开了。代码如下：public static bool transFileToFTP(string filePathp_source, string filePathp_aim, string uploadURIp, string userNamep, string passwordp, string EncryptKey, out Exception e)
        {
            //userNamep = ConvertUserName(userNamep, CONVERT_USER_EXTENSION);
            //passwordp = ConvertPasswd(passwordp, CONVERT_PASS_EXTENSION);
            try
            {
                Exception aa = new Exception();
                FileInfo sourceFileInfo = new FileInfo(filePathp_source);
                FtpWebRequest transFileRequest = (FtpWebRequest)WebRequest.Create(new Uri("ftp://" + uploadURIp + "/" + filePathp_aim));
                transFileRequest.Credentials = new NetworkCredential(userNamep, passwordp);
                transFileRequest.KeepAlive = false;
                transFileRequest.UseBinary = true;
                transFileRequest.Method = WebRequestMethods.Ftp.UploadFile;
                transFileRequest.ContentLength = sourceFileInfo.Length;
                byte[] buffer = new byte[2048];//指定缓存
                int bufferCount = 0;
                int contentLength;
                using (FileStream fs = sourceFileInfo.OpenRead())//将本地文件读入到流中
                {
                    // 获取已上传部分文件大小
                    long existedFileSize = GetFileSize(filePathp_aim, uploadURIp, userNamep, passwordp);
                    // 本地流中远程文件已经写入的部分大小
                    long repeatDataLength = 0;
                    using (Stream uploadStream = transFileRequest.GetRequestStream())//得到ftp服务器返回的流
                    {                        //--将从本地文件的流中读出的数据写入ftp服务器返回的流中--
                        contentLength = fs.Read(buffer, 0, buffer.Length);
                        long filePos = 0;
                        while (contentLength != 0)
                        {
                            if (repeatDataLength > 0)
                            {
                                uploadStream.Write(buffer, (int)repeatDataLength, contentLength - (int)repeatDataLength);
                                repeatDataLength = 0;
                            }
                            else
                            {
                                uploadStream.Write(buffer, 0, contentLength);
                            }
                            contentLength = fs.Read(buffer, 0, buffer.Length);
                            filePos += contentLength;
                        }
                        try
                        {
                            //--将从本地文件的流中读出的数据写入ftp服务器返回的流中--
                            if (!uploadStream.Equals(null))
                            {
                                uploadStream.Flush();
                                uploadStream.Close();//关闭从ftp服务器返回的流
                            }
                        }
                        catch
                        {
                        }
                    }
                    try
                    {
                        fs.Flush();
                        fs.Close();//关闭本地文件的流
                    }
                    catch
                    {
                    }
                }
                e = aa;
                return true;
            }
            catch (Exception es)
            {
                //throw new Exception(es.Message);
                e = es;
                return false;
            }
        }