Thanks. All the validation was saying was that an error of Type 1 occurred. I don’t know what that means.
As I was poking around the unzipped folder, I noticed symbols replacing the dash in the xhtml names. Could my problem have been that my ID file names for each chapter had a dash in it? The first book’s file names had hyphens instead, and those seem to have spit out okay into xhtml file names. I copied all the files into a test folder, renamed them without dashes (no hyphens either), replaced the chapters inside the indb, updated the TOC, and exported to EPUB. Now it is working to unzip/zip. iBooks opens a working file, and it is also validating. So were the dashes in file names the whole problem?
My biggest problem in that test “solution” is that it broke all of my external text anchor hyperlinks. I don’t see a way to simply rename the chapter titles in my original indb without having to Replace them. Is there a way to rename that won’t break external text anchor hyperlinks? Or is there a quick way to wisen up the anchor destination names? I’d love to save a couple hours of redoing those.