Bob got it!! I thought I'd gotten all of the "suspect" characters out, but when he said spaces, I thought of characters/symbols that my Mac will accept but which Windows won't. I went in and checked, and sure enough - the images exhibiting the problems have either a '/' or a '&' in them. Like I said, I thought I'd gotten all of those corrected. :( At least I know what's wrong now. Thanks, guys!
Now, do either of you happen to know if I can do that renaming within the galleries that have been created? Or will I have to rename the pictures and then rebuild the galleries? I can see where it would be kind of a pain to locate each spot where renaming has to happen. Maybe I'll just experiment. Rebuilding the galleries will be the pits, too, because all of those names, dates, and locations will have to be added again. Rats.
(It's interesting, though, that thumbnails will load of a couple of those images. ??)
Now, Grant, you mentioned case sensitivity. What do I have to watch for on that subject? I don't think it's part of my current "issue", but I might as well check that, too, while I'm at it - and add it to the list of "no-nos" when doing work I want viewable on either a Win machine or the web.