[VB] Problem

Option Strict On
Imports System.Net


Public Class Form1


    Public WithEvents download As WebClient


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        download = New WebClient


        Dim URL As String = TextBox1.Text
        Dim ZIEL As String = TextBox2.Text


        ProgressBar1.Value = 0


        Try
            download.DownloadFileAsync(New Uri(TextBox1.Text), ZIEL & Namenberechnen(URL))
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical)
        End Try
    End Sub


    Function Namenberechnen(ByVal url As String) As String
        Dim name As String = Nothing
        Dim stelle As Integer = url.LastIndexOf("/")
        name = Mid(url, (stelle) + 1)
        Return name
    End Function


    Private Sub download_DownloadFileCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs) Handles download.DownloadFileCompleted
        MsgBox("Download abgeschlossen!", MsgBoxStyle.Information)
    End Sub


    Private Sub download_DownloadProgressChanged(ByVal sender As Object, ByVal e As System.Net.DownloadProgressChangedEventArgs) Handles download.DownloadProgressChanged
        ProgressBar1.Value = e.ProgressPercentage
        Dim totalbytes As Long = CLng(e.TotalBytesToReceive / 1024)
        Dim bytes As Long = CLng(e.BytesReceived / 1024)
        Label3.Text = CStr(bytes) & " % von " & CStr(totalbytes) & "%"
    End Sub


    Private Sub TextBox2_MouseDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles TextBox2.MouseDown
        If e.Button = Windows.Forms.MouseButtons.Left Then
            Dim folder As New FolderBrowserDialog
            If folder.ShowDialog = Windows.Forms.DialogResult.OK Then
                TextBox2.Text = folder.SelectedPath & "\"
            End If
        End If
    End Sub


    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged


    End Sub
End Class