My iPad mini is about 4 years old. I am suddenly unable to download books from iBooks. The book begins to download and even shows up in my library, but then disappears and I get an error message that says "unable to load book because required resource is missing". How can I get the "required resource"? I've tried shutting the iPad off completely, then restarting and trying again.
iPad mini Wi-Fi + Cellular (MM), iOS 8, upgraded to OS 8.0.2
