I ran into this issue last week after updating my Kindle, and it was frustrating. The 'can't register' error usually pops up when there's a glitch in the software update or a problem with Amazon's servers. First, I tried restarting my Kindle by holding the power button for 40 seconds, which sometimes fixes minor bugs. If that doesn't work, checking your Wi-Fi connection is crucial because a weak or unstable connection can prevent registration. I also made sure my Amazon account credentials were correct. If none of these steps help, deregistering and then re-registering the device through the settings menu often resolves the issue. It’s annoying, but these fixes usually work.
Another thing to consider is whether your Kindle’s software is fully up to date. Sometimes, incomplete updates cause registration problems. I went to the settings and manually checked for updates, which fixed the problem for me. If you’re still stuck, contacting Amazon support is the best move. They can check if there’s an outage or guide you through more advanced troubleshooting.