[KevinH]

Did you run epubcheck? There is an epubcheck plugin for Sigil to make this easy.

I just tried both an epub2 and an epub3 (our new user's guide) in Sigil with EpubJSReader plugin and they both worked flawlessly. There is a TOC icon in the upper left corner, that will produce a sidebar with the TOC properly nested. As I move my mouse over, the TOC entries they get highlighted. If I click on one, the book is moved to that place properly.

So it is working for both epub2 (toc.ncx) and epub3 (nav).

That is why you need to check it with epubcheck (unless that is identical to the idpf validator link) to detect things like missing nav properties on manifest items, etc.

So there is something specific about that epub that is creating the problem as well formed epub2 and epub3 seem to work fine in EPUBJS. I also tried a html toc and those links all worked as well.