FTP vb.net

Imports System.IO

Public Class Form1
    Private FTPDownloader As New Utilities.FTP.FTPclient

    'Avvio il programma e setto i campi "Username", "Password", "IP Server"

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        TextBox2.Text = "Gianfranco"
        TextBox3.Text = "**************"
        TextBox4.Text = "**************"
    End Sub


    ' Premendo il tasto "Connetti" o Button1, avvio la connessione FTP in attesa venga accettata dal server

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Try
            FTPDownloader.Hostname = TextBox4.Text.Trim
            FTPDownloader.Username = TextBox2.Text
            FTPDownloader.Password = TextBox3.Text
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub



    'Mostro a schermo i file contenuti all'interno della directory indicata

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        FTPDownloader.CurrentDirectory = "/Concerti"
        RefreshList()
    End Sub

    Private Sub RefreshList()
        ListBox1.Items.Clear()
        Try
            For Each file In FTPDownloader.ListDirectoryDetail()
                ListBox1.Items.Add(file.Filename)
            Next
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub


    'Avvio il download del file interessato...qui avviene l'errore misterioso

    Private Sub ListBox1_MouseDoubleClick(sender As Object, e As MouseEventArgs) Handles ListBox1.MouseDoubleClick
        Try
            If MessageBox.Show("Sei sicuro di voler scaricare il download selezionato? " & ListBox1.SelectedItem, "Conferma", MessageBoxButtons.OKCancel, MessageBoxIcon.Question) = DialogResult.OK Then
                FTPDownloader.Download(ListBox1.SelectedItem, My.Computer.FileSystem.SpecialDirectories.Desktop + "\" + ListBox1.SelectedItem)
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub
End Class