Can you be more specific as to when you get this error?
BasePage is a class file you added yourself. Do you have it under App_Code/BasePage.vb
Also, how did you open the project's source that came with the book? If you open it as a Web site, it compiles fine for me and BasePage can be found.
If you provide more detail (detailed steps, VS version, how you're opening the site, when/where you get the error) I might be able to help you better.