Myself and a handful of N5 users on the Android M developer build are getting an "unknown error" on all Amazon apps that check back with the app before unlocking. As far as I can tell, there's no way around it currently, so don't bother uninstalling, clearing data, reinstalling, or any permutation of those actions.

I've contacted Amazon and was told that my issue would be forwarded to the techs, so here's hoping for an eventual fix.

For reference - this is the error you'll get. The app loads in the background, but the check stops it from unlocking.

I can't vouch for the other people having this problem, but I personally did a full, clean install of M and installed all of my apps from scratch.

I'm aware that this is a developer build and there will be bugs, but I figured the information would be helpful to people looking to try the dev build or who are already on the dev build and use Amazonia service.