HTML parsing using mshtml causing exceptions on Windows XP SP2

Private Declare Function GetForegroundWindow Lib "user32" Alias "GetForegroundWindow" () As Integer
 
    Public Class Window
        Public BodyHtml As String
        Public LocationName As String
        Public Url As String
        Public Hwnd As Integer
    End Class
 
    Public Class InternetExplorerWindows
 
        Public Shared Function GetWindows() As List(Of Window)
 
            Dim list As New List(Of Window)
            For Each window As InternetExplorer In New ShellWindows()
 
                ' Skip Windows Explorer instances, since the Document type is IShellFolderViewDual2.
                If TypeOf window.Document Is mshtml.HTMLDocument Then
 
                    ' Get the HTML document represented by the browser's Document property.
                    Dim doc As mshtml.HTMLDocument = CType(window.Document, mshtml.HTMLDocument)
 
                    ' Create a class to collect important information to return to the caller
                    Dim win As New Window()
 
                    If doc.getElementById("TargetContent") IsNot Nothing Then
                        ' Get the HTML from the IFrame element, if it exists.
                        Dim frame As mshtml.HTMLIFrame = CType(doc.getElementById("TargetContent"), mshtml.HTMLIFrame)
                        Dim windowDocument As mshtml.HTMLDocument = CType(frame.contentWindow, mshtml.HTMLWindow2).document
 
                        win.BodyHtml = windowDocument.body.outerHTML
                    Else
                        ' Get the HTML from the main document.
                        win.BodyHtml = doc.body.outerHTML
                    End If
 
                    ' Store info needed from the Internet Explorer instance.
                    win.LocationName = window.LocationName
                    win.Url = window.LocationURL
                    win.Hwnd = window.HWND
 
                    list.Add(win)
                End If
            Next window
            Return list
        End Function
    End Class
    Private Sub hotKey_Pressed(ByVal sender As System.Object, ByVal e As HotKeyPressedEventArgs)
 
        Dim windowList As List(Of Window) = InternetExplorerWindows.GetWindows()
        Dim activeHwnd As Integer = GetForegroundWindow()
 
        For Each win As Window In windowList
            Dim html As String = win.BodyHtml
            Dim id As String = HtmlParser.FindIntegrationID(html)
 
            If id.Length > 0 AndAlso win.Hwnd = activeHwnd Then
 
                txtPropertyValue.Text = id
 
                Dim sURL As String
                sURL = constructURL()
 
                OpenBrowser(sURL)
 
                Exit For
 
            End If
        Next win
 
    End Sub
 
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Me.Close()
    End Sub
 
    Friend Class HtmlParser
 
        'This is the main logic for the PeopleSoft scrape. Parse through the HTML looking for the required data.
        ' Look for:
        ' <label for='VOUCHER_PACKSLIP_NO' class='PSEDITBOXLABEL' >Integration ID</label>
        ' </td>
        ' </tr>
        ' <tr>
        ' <td height='51' colspan='2'></td>
        ' <td colspan='4'  valign='top' align='LEFT'>
        ' <span class='PSEDITBOX_DISPONLY' >000000010001</span>
 
        Public Shared Function FindIntegrationID(ByVal pageText As String) As String
            Dim document As New mshtml.HTMLDocument()
 
            ' The HTML document class doesn't have the correct 'write' method, 
            ' so use the IHTMLDocument2 interface.
            CType(document, mshtml.IHTMLDocument2).write(pageText)
 
            Dim labelFound As Boolean = False
            Dim count As Integer = 0
 
            For Each table As mshtml.HTMLTable In document.getElementsByTagName("table")
 
                If table.className = "PSPAGECONTAINER" Then
 
                    ' Loop through all the table cells (<td> elements)
                    For Each cell As mshtml.HTMLTableCell In table.getElementsByTagName("td")
 
                        If Not labelFound Then
                            ' Look for the last 'Integration ID' label, since we need the lowest
                            ' level <td> element.
                            For Each label As mshtml.HTMLLabelElement In cell.getElementsByTagName("label")
                                If label.innerText = "Integration ID" Then
                                    If count < 4 Then
                                        count += 1
                                    Else
                                        ' The right <label> was found, so quit looking, and start looking for the next <span>.
                                        labelFound = True
                                        Exit For
                                    End If
                                End If
                            Next label
                        Else
                            ' The next element that has a <span> child should be the 'Integration ID' value.
                            For Each span As mshtml.HTMLSpanElement In cell.getElementsByTagName("span")
                                Return Format(Val(span.innerText), "000000000000")
                            Next span
                        End If
 
                    Next cell
 
                End If
 
            Next table
 
            Return ""
 
        End Function
 
    End Class
 
End Class