I think I figured this out, but I'd love to hear an opinion from an expert. I was previously saving the files by right clicking on the link to the file from the book's main page and choosing "save as" **But** then I tried going ahead and opening the link and saving the page from the file menu, after I already had it up on my screen (make sense?). Those files that I saved that way worked!! Yeah!!!
Now. If I only knew why?!? :-)