Installed new image... server refused our key...?

Operating system and version Ubuntu Core 16

Is this the first time you’ve seen this error?:yes

Can you reliably replicate it? yes

The issue you are facing:

I set up the sd card and the server the new way (https://github.com/nextcloud/nextcloud-snap/wiki/How-to-connect-to-the-Nextcloud-Box-with-SSH):

  1. created a account
  2. validated e-mail
  3. created ssh-key via puttygen
  4. uploaded the public key on ubuntu-account
  5. startet the server and OOBE-Setup
  6. get an informationen, that the setup was successful
  7. using putty on windows - added the key (ssh auth) and login…

but: the server replied: server refused our key

How can I solve the problem?

Thank you!

Greetings!

Michael