Yes it was entered into the TOC before importing.
File name and case is the same,
I did not have a duplicate name but may have a different issue.
The chapter that does not get imported was shown as " Firefox document" that would open with Firefox. All the others are listed as HTML files, that open with Jarte, which is simply wordpad with spell checker. I opened the firefox document with Jarte and saved it as HTML, which worked. That file looks like the others, but I did not do a detailed line by line comparison.