First, thanks for buying the book! I'm glad you are finding it useful. :)
My first thought is that you stumbled across one of the (hopefully) few mistakes I made in the text, as is highlighted in the errata:
I had the section on securityTrimmingEnabled in Chapter 6 (look for the errata items from 9/27). Look over what I corrected and see if that works.
Honestly, I haven't seen that error before but see if the errata text helps fix your problem. If it doesn't, can you post the relevant code? I am sure we can figure it out.