Do you have an ereader?

[Catrin]

The native file type for Nook books is epub, so if it is messed up in your Nook software it likely will be messed up anyway. If you purchased the ebook directly from the publisher there may, or may not, be DRM issues - but if that was a problem then I would expect you to have had an error message directly related to that.

You may have better luck with the Calibre software - I use that to convert ebooks (without DRM protection) between my various ebook format where possible. You can use it to read ebooks, so give it a shot. BTW, I've a Samsung Galaxy Tab 4 that I use to read my Nook books these days since my Nook died and I moved on to the Kindle Paperwhite. I think sometimes there are problems with large, complex texts that a publisher has made available on epub because they don't stop to consider some the the special elements needed for an ebook environment. I mean the ability to change font size, border size, how the text flows, etc. This is why it can be dicey to convert a PDF to e-book formats as well.

Hopefully some of that helped at least a little, I share your pain on this.