This happens on a particular book or all books? Try giving the touch screen a nice wipe down to clean off any possible smudges and such. If still a problem, perhaps a hard shut down and turn on will help.
I have had this same problem, I have found that when it happens if I just perform a full shutdown (not just putting it to sleep) and rebooting has solved my problem.
I hope this helps.
I've been having the same problem with one book. I will be reading along, and then suddenly, the book will loop back about 4 or 5 page, and it will just keep doing that.
I fixed this issue by completly shutting down my nookColor and "rebooting" it. The book doesn't loop anymore, but there is a problem that has been plauging it since I downloaded the book.
For this book, when I go to the appendix, it shuts the reader program down. I can't view the appendix at all. I can view it on the nook for PC program, but not on my nookColor. I can't figure that one out.