The third book written by Jason Bubsy, Zak Parrish, and Joel VanEenwyk in the Mastering Unreal Technology Series has been canned.
The Mastering Unreal Technology book series is an educational set of books meant to teach user’s to use and master the Unreal Development Kit, the third one specifically for scripting in the engine. According to Zak Parrish, the book was finished a very long time ago, however the publisher never got it out the door. Now, the Unreal Engine is updated and changed so often, it would be very difficulty to keep up with it while trying to publish a book. Unfortunately, they will not be able to release all of the information that was contained in the book, because it was written under a contract with the publisher.
Parrish did state however, that at least half of the books text is already available on the UDN website.
You can read the original posting of the cancellation by Zak Parrish, Here.