Thanks, Nigol, for the update. And thank you, Nick, for the excellent rendition of "Lorna Doone."
It's apparent to me that I'm doing something wrong. I can use epubfixer to create a new TOC and save the file ... works beautifully. However if I make any subsequent modification to the text itself (using epubfixer or not) , and then save the modified file, the new TOC no longer works. Depending on how I've done the modifications, either my changed TOC disappears or if it is still there, clicking on a TOC entry results in incorrect results or an error message.
If I re-edit to Nick's new version of "Lorna Doone," the results are fine.
I've attached my epubfixer fixed version of a Project Gutenburg epub book by Thornton Burgess. Perhaps someone out there can tell me what I'm overlooking.
Thanks for any help.