I was working with support to be able to ssh to the our vCenter 5.5 VCSA. No matter what account we were trying to reach, we would immediately get a popup saying: "Server responded: Algorithm negotiation failed. Key exchange with the remote host failed".
He had me download putty and try it, and I was stunned to find that it worked.
We normally use "SSH Secure Shell" from www.ssh.com (V 3.2.0) for all our ssh sessions from Windows to Linux. But in this case, it won't work. I did find a (non vSphere) forum post saying a guy got the same error when he used a commercial ssh client to reach an OpenSSH server. My ssh client says it's "a non-commercial version which does not include PKI and PKCS #11 functionality"
My thanks for any ideas....Lyle