I was using my iPhone 4s and playing a game of solitaire when I got a totally unrelated error message out of nowhere.It was something like "the book you are trying to download (or open?) can only be used with an iPad". Obviously I don't have the message exactly right but it was along those lines.
I just hit OK and then looked to see if another app was open, but found only the solitaire game. I opened iBooks to see if it was trying to DL and the iTunes U, then the App store to check if it was trying to do anything or any available updates. Nothing going on there.
Then it happened again a few minutes later!
I fully powered off the phone and restarted it this morning, looked to see if apps were trying to download etc, found the App store had an update for iTunes U.
Related somehow??