Originally Posted by geekmaster
That is the obvious first fix for most tech devices. But I guess we need to say it anyway. I would avoid the SECOND standard method of fixing misbehaving devices (giving them a good solid whack) because that could easily damage the eink screen.
My suggestion was meant seriously though. I have also seen this happening (couldn't open anything, same message as the OP stated), and restarting the device fixed it.