Permission denied (publickey).

After successful configure github access using Win/msysgit I have to fight on the Linux front. Just copy the private key file generated with puttygen didnt work:

[thomo@sun .ssh]$ ssh git@github.com
Enter passphrase for key '/home/thomo/.ssh/thomo__github_private.ppk':
Permission denied (publickey).

I neither enter a passphrase nor was able to change the empty phrase using ssh-keygen -P. :-|

To solve the problem I export the private key in OpenSSH format: