Originally Posted by Unforgiven
Unless you have sideloaded it, the Kindle doesn't come with Play. It is a fork of Android so may not be compatible.
That may be it. It's a Google Play app.
Also, WCGrid tweeted earlier today, World Community Grid Will be down From Jan 22 - 24 not downloading or sending any Work Units.
They are down for Fixing, sorta like this site is sometimes.