I just started reading this book so I can't give you an answer, but maybe I can offer a suggestion. Try doing a clean and full rebuild of the solution. (Introduction pg xxviii). Hope that helps!
EDIT: I experienced the same error building one of the samples from chapter 4. Clean and rebuild corrected the issue.
For those who may not know how to perform the appropriate action:
Confirm you are in Debug configuration (usually a drop down selection on the menu at the top of the screen).
In solution explorer (View -> Solution Explorer) right click on the solution.
Click "Clean Solution".
When that completes click "Rebuild Solution".
After that you should be able to proceed as usual.
Last edited by bhall066; September 24th, 2012 at 06:14 PM.