Not necessarily a compatibility issue, but a conversion issue. I'm assuming that you opened the WSI test application in Visual Studio 2008, which automatically caused a conversion to take place, yes? Then you used that as the basis for creating your test app?
The issue here is that the WSE references in the Reference.cs file were automatically removed during the conversion process. If you grab the Reference.cs file from the app you converted and the Reference.cs file from the original WSI test application and compare them (just grab a free copy of WinMerge and do a quick file diff), I bet you'll find that the WSE methods and references are missing from the converted file.
You can either merge over the original lines (careful here though...this file is easy to mess up) or just copy the original Reference.cs file into the new application (assuming you haven't made any changes)
<a href="http://www.aspdotnetstorefront.com">Shopping Cart Software</a>