Customers using an outdated software version on Kindle e-readers require an important software update by March 22, 2016 in order to continue to download Kindle books from the Cloud, access the Kindle Store, and use other Kindle services on their device.
If you do not update your device by March 22, 2016, you will receive the following message on your device: Your Kindle is unable to connect at this time. Please make sure you are within wireless range and try again. If the problem persists, please restart your Kindle from the Menu in Settings and try again. If you see this message on your device on or after March 22, you will need to manually install the latest software update for your device.
I can’t imagine what changed on Amazon’s end that requires an update like this, across almost every generation of device.