WebBrowser and Excel, depending on location code, occurs Exceptions...

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C#

WPF

MS-Excel

web_browser

Hi all

I am using VS2008, C#, with WPF application (WebBrowser and Microsoft.Office.Interop.Excel)
I have a task : Hosting Excel on WPF-form in mode readonly.

How can I do this:

if ((WebBrowserExcel.Document as Excel.Workbook) == null) return;
   try
   {
      _Book = WebBrowserExcel.Document as Excel.Workbook;
      _Book.Protect("", Type.Missing, Type.Missing);
      foreach (Excel.Worksheet _sheet in _Book.Sheets)
      {
            _sheet.Protect("", Type.Missing,Type.Missing,
                          Type.Missing,Type.Missing, true,Type.Missing,
                          Type.Missing, Type.Missing, Type.Missing, 
                          Type.Missing, Type.Missing,Type.Missing,
                          Type.Missing, Type.Missing, Type.Missing
      );
   }

   //In this moment - Exception
   _Book.Application.GetType().InvokeMember("DisplayAlerts", BindingFlags.SetProperty, null, _Book.Application, new object[] { false });

If I place all code in the Startup Windows (StartUpWindow) of Project - works well, but if I place all code in the other window (Window1) and show this window from Startup (Window1.Show())

private void btn_ViewExcel_Click(object sender, RoutedEventArgs e)
{
       Window1 _W1 = new Window1();
       _W1.ShowDialog();
 }

- works badly:

InnerException = {"could Not set the property DisplayAlerts Application class"}

Because of what it can be?
Thanks in advance, Alex...