It sounds as if you are having an issue with the download of the file.
A quick fix:
1) Open your library and hold down the book title that is having the issue.
2) Select Archive from the menu that appears (be careful to not press Delete). The book will disappear, but it is not gone from your account.
3) Next, on the top row of options in your library, select My Stuff and then Archived. Your title should be listed in this section.
4) Hold down the book title again and select Unarchive. You must be in a wi-fi area to do this; the book will re-download. This should fix the bug in the file.
**If you are worried that the minor spill your device had is affecting your Nook's performance, bring it in to the nearest Barnes and Noble for assistance. I hope this helps.
I just experience an odd bug where page turns would bring me to a page other than the one that is supposed to come next. Sometimes it skipped forward a few pages. Sometimes it actually went backwards. Most commonly it kept bringing me to the same page I just left. I was worried, because the tablet took a minor fall about half an hour prior to this, and I haven't seen any mention of this happening to anyone else online.. A soft reset seems to have fixed it though, so I'm guessing it was a software problem and not a hardware one. Is this a known problem with the Nook Tablet?
This is a known problem in the Nook Color 1.4.x firmware. So probably also in the Nook Tablet firmware.
A reboot usually solves the problem.
As an occasional ebook publisher I have found that there seems to be some problems with how the Nook handles text flows with long paragraphs. In particular, if the epub file has an image in a paragraph, and the image is taller than the Nook display height, the 'page turn' function tries to go to the next page (or back to the previous one), and then it discovers that it still has a bit of that image to display, so it displays the whole thing, and you end up in an endless loop stuck on the same page. The same thing seems to more rarely happen with long text paragraphs. That's why changing the font size can help, as the software will then have to re-render and reflow all the text. It's very annoying because neither the Kindle or iPad have this issue.
That is to say, we build a clean epub file (which we validate against the standard epubcheck tool), load it to various Kindles and the iPad, and it looks great, but when we load it onto the Nook, we have this problem, which we consider unacceptable. There seems to be some fairly major issue with the way the Nook implements pagination within paragraphs and I can't say that we've figured it out yet.