Strange, it looks to me like this code shouldn't work in any VB project that
automates PowerPoint, regardless of the version of Visual Studio being used.
There is no class called "ActiveWindow" in the
Microsoft.Office.Interop.PowerPoint namespace. However, there is an
Application.ActiveWindow property.

I think the following code accomplishes what you are really trying to do.
This code works for me in a PowerPoint add-in created in Visual Studio 2008:

       Dim ActWinSlideRange As
Microsoft.Office.Interop.PowerPoint.SlideRange = _
           Me.Application.ActiveWindow.Selection.SlideRange

I hope this helps,
McLean Schofield