I've always gone back and forth between my current book and Words with Friends by touching the book icon on the bottom left. Suddenly I get a message "sorry, the content you're attempting to open is no longer available" and I have to press the n button > library> the book. I know that's not a huge deal, but I haven't had error messages often before and I'm a bit too compulsive to just ignore it. This happened a few days ago, then I updated Words with Friends and it still continued.
In settings, tap home, clear keep reading list. Open book, close book. Tap keep reading book icon or keep reading on top of home page. Not sure what causes the error message, but this should fix it.
