Hello!

I'm doing a small download manager, but I was stopped by a little problem xD
So I wanted to add all links to download in a listbox, and download them one at a time not all at once.

This is the code that has the problem NotSupportedException:
Code:
    Private Sub down_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles down.Click
        download = New WebClient
        Dim save As String
        Dim ab As String
        save = urltxt.Text.Split("/"c)(urltxt.Text.Split("/"c).Length - 1)
        If urltxt.Text = "http://" Then
            MsgBox("Riempi l'url!!", MsgBoxStyle.Critical)
        Else
            For Each itm As String In ListBox1.Items
                download.DownloadFileAsync(New Uri(itm), brwtxt.Text + save)
            Next
        End If
    End Sub
I said that does not support I / O operations simultaneously, but the problem is that I do not want to do any simultaneous action I just want you download the first link when finished proceed to the second, etc.

What's wrong?