I downloaded a new book on my Nook and also on the Nook app on my iPhone. It works on the Nook Color but when I open the book on my phone it is blank page after blank page.
I can open and read other books, just not this one. It was downloaded from B&N as well as another book at the same time and the other one is fine.
I once had a book that would not work if my iOS Nook app was set to night mode (black screen with white text). I worked fine in day or gray setting. I don't remember which book it was, but it took me a while to figure it out. That is the only thing I can think of. You might try archiving it and redownloading it too see if maybe the file was corrupted.