Sigil Crashes when creating HTML ToC

I'm running Sigil 0.9.8 to format an epub 3.0 file that was created in InDesign CC. I've done this a dozen times, but this one book keeps crashing. I've got everything thing done, all the formatting, the TOC generated, but when I go to create the HTML table of contents, one of two things happens. Either the HTML TOC overwrites the entire file, so that I only have the TOC but no content, or Sigil just crashes. This has happened over a dozen times now.

Any clues as to what might be the problem?