SSH: Agent admitted failure to sign using the key.

When you are trying to ssh to a remote server using passwordless login, you might get an exception
   "Agent admitted failure to sign using the key."

Issue may be the private key is not properly added (default location : ~/.ssh/id_rsa )

To fix the issue, (preferably in a separate terminal) issue the following command
    $ ssh-add

This will add the private key giving the output "Identity added: /home/wso2/.ssh/id_rsa (/home/sajith/.ssh/id_rsa)"

Now you can ssh to the remote server as expected...
     $ ssh user@remoteserver