If you just upgraded Ubuntu 15.04/10 to Ubuntu 16.04 LTS (or otherwise upgraded OpenSSH from v6.9 to v7.0 you may be getting the ssh refusal because of changes in OpenSSH.
I was specifically getting this error in the /var/log/auth.log (via Webmin): sshd[2444]: userauth_pubkey: key type ssh-dss not in PubkeyAcceptedKeyTypes [preauth].
For this specific error, you need to add “PubkeyAcceptedKeyTypes=+ssh-dss” (without the quotations) to the bottom of your /etc/ssh/sshd_config file.