That's sounds like it almost has to be an Amazon server side issue, not a problem with the devices. Maybe someone from the dev section can correct me, but I can't think of why the device would discriminate samples from other content.
If amazon can't find a solution, you could always try the Microsoft approach...turn it off then on again.
Do a hard reset, remove and re-regester it to you account. Seriously, other than re-flashing the firmware there isn't all that much to try on the device side.