Ssh login failure

Recently I had a problem logging into a server using ssh.  I setup the public key as usual as an authorized key on the server but kept seeing an "Agent admitted failure" message.

$ ssh server.domain.com
Agent admitted failure to sign using the key.
Permission denied (publickey,gssapi-keyex,gssapi-with-mic).

The fix was to update the ssh-agent as follow:

$ ssh-add
Enter passphrase for /home/rrosso/.ssh/id_rsa:
Identity added: /home/rrosso/.ssh/id_rsa (/home/rrosso/.ssh/id_rsa)

$ ssh server.domain.com
Last login: Mon Jan 14 18:01:31 2013 from .hstntx.sbcglobal.net