FTP client vb.net error

Private Sub listFTP(ByVal URL As String, ByVal bk As String, ByVal pw As String)
        Dim requ As FtpWebRequest = Nothing
        Dim resp As FtpWebResponse = Nothing
        Dim reader As StreamReader = Nothing
        Try
            requ = CType(WebRequest.Create(URL), WebRequest)
            requ.Credentials = New NetworkCredential(bk, pw)
            resp = CType(requ.GetResponse(), FtpWebResponse)
            reader = New StreamReader(resp.GetResponseStream())
            While (reader.Peek() > -1)
                ListBox1.Items.Add(reader.ReadLine())
            End While
            StatusBar1.Text = "Refresh Succeed!"
        Catch ex As UriFormatException
            MsgBox(ex.Message)
        Catch ex As WebException
            MsgBox(ex.Message)
        Finally
            If reader IsNot Nothing Then reader.Close()
        End Try

    End Sub