VB.NET Webbrowser and WIN. VISTA

Hi all.I have A problem.
This is Code:

Private Sub WebBrowser1_DocumentCompleted(ByVal sender As System.Object, ByVal e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted

        If WebBrowser1.Document.Body.OuterText.Contains("Personal Data") Then
            RichTextBox2.Text = RichTextBox2.Text & vbNewLine & "i'm Here!"
            Timer1.Stop()
            Timer2.Start()
        End If
       
    End Sub

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Private Sub Timer2_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer2.Tick
        Try
            WebBrowser1.Navigate(ListBox2.Items.Item(0).ToString)
            RichTextBox2.Text = RichTextBox2.Text & vbNewLine & "Going To: " & ListBox2.Items(0) & "!"
            Timer2.Stop()
            Dim ts As TimeSpan
            Dim targetTime As DateTime = DateTime.Now.AddSeconds(3)
            Do
                ts = targetTime.Subtract(DateTime.Now)
                Application.DoEvents() ' keep app responsive
                System.Threading.Thread.Sleep(50) ' reduce CPU usage
            Loop While ts.TotalSeconds > 0
        Catch ex As Exception
        End Try
        Timer2.Stop()
        If WebBrowser1.ReadyState <> WebBrowserReadyState.Loaded Then
            Timer4.Start()
        End If
    End Sub

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It's Working perfectly On Windows 7 x64
But on other OS(Win.XP,WIN.VISTA) it's not working.
What's The problem??
Thank's