使用vb.net使用FtpWebRequest在电子邮件中附加多个FTP文件

Question

 Dim taskResults As IList(Of Task) = New List(Of Task)()           
        Try
            For Each row As DataRow In filesTable.Rows
                fileName = row("Name")
                Dim request As FtpWebRequest = WebRequest.Create(Convert.ToString(ftp & ftpFolder) & fileName)
                request.Method = WebRequestMethods.Ftp.DownloadFile

                'Enter FTP Server credentials.
                request.Credentials = New NetworkCredential("ksmusic", "Kevin2009")
                request.UsePassive = True
                request.UseBinary = True
                request.KeepAlive = True

                Try
                    taskResults.Add(Task.Factory.StartNew(Function()
                                                              Dim response As FtpWebResponse = request.GetResponse()
                                                              contentStream = response.GetResponseStream()
                                                              mailMessage.Attachments.Add(New Attachment(contentStream, fileName))
                                                          End Function))
                Catch ex As Exception
                    Dim err As String = ex.Message
                End Try
            Next row

我遇到以下错误：- 在上一个呼叫仍在进行中时无法重新调用BeginGetRequestStream / BeginGetResponse。 有时我得到：-远程服务器返回错误：（530）未登录。

请让我知道如何管理并发。

谢谢