系统找不到ftp 550错误中指定的路径

Question

试             {                 _ftpClient = ConnectToServer（_ file，_FtpType，_DbOperations，_ftpClient）;

            if (_ftpClient == null)
                return "";


            _ftpClient.Method = WebRequestMethods.Ftp.Rename;
            _ftpClient.UsePassive = true;
            _ftpClient.KeepAlive = false;
            _ftpClient.UseBinary = true;
            _ftpClient.RenameTo = "../" + _FtpType.P_SourceFolderTemp + "/" + _file;
            _ftpClient.GetResponse();
            return "1";
        }
        catch (WebException ex)
        {
            string hata = ((FtpWebResponse)ex.Response).StatusDescription;
            //_DbOperations.Logla(_BBSFtpType, "j");
            _DbOperations.DbExceptions(_BBSFtpType);
            return "0";
        }

程序属于catch状态描述为550-系统找不到指定的路径.Win32错误：系统找不到指定的路径。错误详细信息：文件系统返回错误.50结束。我该怎么做才能纠正它？