Ubuntu – putty key -> connection refused (permissions OK, /var/log/auth.log is empty)

I already checked here:
Trying to do ssh authentication with key files: server refused our key

and I did all these:

*new:

• generated key(s) via ssh-gen in a Linux client.
  • added the public key to the server via ssh-copy

now I don't see any error message,
here's ssh -vvv:
http://pastebin.com/Cxspz5P3

Could it be that there's an order to the authentication process, but the server first tries to verify password, instead of trying out the publickey?

Original post: what I tried so far:

• generated key(s) via puttygen (v.2015-12-03) in the windows client:

  • 2048 bits, and tried also key-pair with 1024 bits

• copied "openssh public key" in 1 line format from puttygen,

  • the line that looks like:

    ssh-rsa xxxx... ==
    

  • pasted it to the ubuntu server to ~/.ssh/authorized_keys

  • one line for the 2048 bit key, additional line for the 1024 bit key

• I changed the file permissions like so:

  chmod 700 ~/.ssh
  chmod 600 authorized_keys
  chmod 700 ~
  chown -R $USER.$USER ~/
  

• putty session settings:

  • 'connection' > 'data' > 'username' > myuser

  • 'connection' > 'ssh' > 'auth' > the PPK file

• tried with both 2048 bit and 1024 keys (with their respective public keys)

• tried also from localhost (ssh -i .ssh/mykey myuser@localhost) – got the same /var/log/auth error:

  Failed publickey for (myuser) from ::1 port 50087
  

• increased log level of /etc/sshd_config: LogLevel VERBOSE (is there higher value?) on the server, and restarted. /var/log/auth.log now gives:

  **Failed publickey for** myuser from xx.xx.xx.xx port xx: RSA xx:xx:xx...
  

systems:

• tried to connect from:
  • from windows (putty 2015-12-3, key is PPK)
  • from linux/mint 17 (via ssh, openssh key)
• server: Ubuntu 14.04.2 LTS
• keys generated by puttygen on windows (v.2015-12-03)
• also tried with "kitty" (a putty fork)
• ssh with password – works. always.

tail -f /var/log/auth.log isn't showing anything for failed logins, only for successful and for logouts.

Can it be cured?

is there another way to diagnose the problem?

Q&A:

Q. What is a "data" connection? Why didn't you use "ssh" in both cases?

A. it's just the section's name in putty config.

Q. cat /etc/ssh/sshd_config|grep -i author

A. AuthorizedKeysFile ~/.ssh/authorized_keys

Q. ls -lZ .ssh (on the server)

drwx------ 2 myuser myuser ? 4096 Dec  5 12:28 .   <---- the .ssh dir
-rw-r--r-- 1 myuser myuser ?  666 Dec  5 12:29 known_hosts
-rw------- 1 myuser myuser ? 1671 Dec  3 12:07 mykey.ssh
-rw------- 1 myuser myuser ?  608 Dec  3 11:47 authorized_keys