[2008] Using MSHTML with Extended Webbrowser. Getting error.

I trying to make form filler, but I faced some difficulties.
There is a greate example in this kleinma`s thread http://www.vbforums.com/showthread.php?t=416275, but axWebbrowser sometimes doesn't fire DocumentComplete event. In that thread, there was said that its much better to use Extended Webbrowser control, because it has advantages of standard Webbrowser and axWebbrowser.
When I trying to do the kleinma`s example actions(for example, set textfield value) with Extended Webbrowser:

Code:

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Private Function GetCurrentWebDoc(ByVal wb As WebBrowser) As MSHTML.HTMLDocument
        Try
            Return DirectCast(wb.Document, MSHTML.HTMLDocument)
        Catch ex As Exception
            Return Nothing
        End Try
    End Function

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I get exception

Quote:

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Unable to cast object of type 'System.Windows.Forms.HtmlDocument' to type 'MSHTML.HTMLDocument'

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Could you tell me, what am I doing wrong?
Thanks in advance.

PS: Sorry for my English...