PS--I removed those references to AmaznRemoved references, then saved, then validated the stylesheet, made a couple of repairs based on error messages, converted the epub to mobi via Kindle Previewer (Looks good on Kindle Paperwhite device and on KP), converted to epub via
www.online-convert, loaded it into my Nook, and it WORKED!! Looked at it on ADE and it, too, worked. It just won't work with an epub produced by Sigil . . .
I continue to get the same error in Sigil check: "OEBPS/Text/part0044_split_000.html" with this explanation: "This OPS document is reachable but not present in the OPF <spine>. "Reachable" means that a reference of some kind that points to this resource exists in the epub." I get this twice because one of the sections of the book had been split for some unknown reason so I put them back together in a single section and renamed it, Part OO44.html. I deleted the two split sections.
I have checked the opf file, the ncx, and the 0044 section, as well as a number of other sections of the book--can't find any reference to these deleted sections. Anything to worry about?