The problem is with the headers of the Toc (cano.ncx file inside this epub). I haven't figured out exactly what is technically wrong with it yet, but the following changes fixex it.
Delete the line: <!DOCTYPE ncx PUBLIC "-//NISO//DTD ncx 2005-1//EN" "http://www.daisy.org/z3986/2005/ncx-2005-1.dtd">
Replace the next line with:
<ncx xmlns="http://www.daisy.org/z3986/2005/ncx/" version="2005-1" xml:lang="en">
Edit: Actually, just adding the missing xmlns="http://www.daisy.org/z3986/2005/ncx/" to the <ncx> element is what's needed to fix this book.
Edit 2: The really gory details:
http://www.idpf.org/epub/20/spec/OPF...Section2.4.1.2