Yes, I agree that it seems like a capacity problem - i.e. the internal html file was just too large for the Nook to handle. This is why I did the split. I think this is an interesting thing to know now, because it seems that people periodically have problems with this, probably mostly with free ebooks produced by amateurs.
Too bad most non-techie folks would probably have trouble fixing the problem in Sigil, I think, even though it's easy enough using the Sigil tool for splitting the current file at the cursor.
Edit: Ideally, IMHO, a book has a split at each chapter and a Table of Contents entry for each chapter. In this particular ebook case, it has very few splits and no table of contents. No wonder it screws up!
Last edited by RAH; 10-14-2012 at 10:41 AM.