Comment 6 for bug 1569019

I have the same problem,

sign_and_send_pubkey: signing failed: agent refused operation

is displayed if i do a ssh connection to a host,
but i am using a yubikey (a gpg enabled hardware key) that delivers the key. and therefore i cannot do ssh-add
i have a running gpg-agent with
echo "enable-ssh-support" >> ~/.gnupg/gpg-agent.conf
"set | grep SSH " is correct
SSH_AUTH_SOCK=/home/user/.gnupg/S.gpg-agent.ssh

the key with ssh worked in all previous versions of ubuntu