I upgraded my first generation iPad to 5.1.1, my Kindle app books "appeared" to all come back. However, I get the error message, "Please remove the book from your device and redownload it from your cloud items. If the problem persists, try to deregister your application and register it again." I have no idea what they are talking about. I do not know how to remove the book, nor do I know how to deregister my application.