SSH can't connect, but output "no kex alg"

Hello, I've got a problem with my ssh/sftp, could some one help me out please? It is like this: I setup the ssh/sftp in the "system preferences", generated the keys with ssh-keygen. But when I use ssh/sftp to connect, it give me a out put "no kex alg", what should I do?

Help, help!

regards, and thank you.