Hi there,
You typically get this error when you open the parent folder of the folder that contains the site. So, if your source is here:
C:\MySites\Chapter6
and then open C:\MySites as a web site in Visual Studio and browse to
http://localhost:123/Chapter6 you get this error. Instead, you need to open C:\MySites\Chapter6 as a web site in Visual Studio and browse to
http://localhost:123/
Hope this helps,
Imar