Ah -- your device was exchanged and blacklisted. So even if you wanted to register you can't.
Downgrading via ixtab's 5.4.0 images should work. It does include an old version of the jailbreak, upgrade that
or a surprise 5.6.x OTA will bork everything.
(Does Amazon send OTA updates to blacklisted devices? I don't see why, but then again I don't see why not...)