The problem is caused by you not defining any \section{}'s in your appendix chapters. Specifically, the mini-toc in the chapter header causes the problem when it's empty. As soon as you define sections like this:
the book will compile just fine. If you don't want sections at all in your appendices I would recommend you implement a flag for turning the chapter header images off in structure.tex. A hint for this is that lines 307 and 308 need to be commented out to remove the chapter header image so you need an if statement there.
Cheers,
Vel
Founder and administrator of LaTeXTemplates.com and LaTeXTypesetting.com