above solution doesn't work for me for unknown reason. below is my workaround which was worked successfully.
1) DO NOT generate a new ssh key by using command ssh-keygen -t rsa -C"xxx@xx.com", you can delete existing SSH keys.
2) but use Git GUI, -> "Help" -> "Show ssh key" -> "Generate key", the key will saved to ssh automatically and no need to use ssh-add anymore.
