Microsoft Web Browser Control & Excel

Configuration: Win XP, IE 6.0, VbB .NET 2003, MS Office 2003

I am developing a win application. It display a excel file in Microsoft Web Browser Control, a COM componenet. I do it as following:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Me.AxWebBrowser1.Navigate("D\test.xls")
End Sub

The code upper can run normally. But if an Excel application has been startup before it, this Excel application can not be operate anymore and be blocked by my new form.

Who can tell me how to resolve this problem? Thanks!!!