If you were assuming that this was going to be a "step-by-step" book with a lot of hand-holding along the way, you'd be mistaken.
You will find that the author indeed skips a lot of "steps" in the explanations. That's on purpose.
The author assumes you will examine the downloaded code, and the book then briefly explains the more complex classes and some of the interesting methods, and steps you through a few of the trickier parts only. The parts that are examined in detail are, for the most part, the new functionality that was introduced in ASP,NET 2.0. Therefore, you won't be able to re-create the code by using the book alone, as most of the non-2.0 legacy code isn't rehashed. It is assumed that the reader possesses a decent understanding of the C# language and .NET framework, at least up to 2.0.
As far as "errors" are concerned, there is a list of errata on this site. First thing you should do is to download that, grab yourself a pencil, go through your book, and correct the known errors before continuing.
If you are having a particular issue, you can ask your question here or at http://forums.asp.net/1115.aspx
and someone will most likely try to help you.