Putty 0.71 SSH connection failure, but 0.70 works

I can successfully use Putty 0.70 to connect with SSH from Win10-x64 to Solaris10-x64 host, using default putty settings. But using Putty 0.71 for same machine & same (default) settings it immediately displays error "Remote side unexpectedly closed network connection". Using latest Putty 0.75 the connection attempt stalls, never finishes, no output and no errors. Any ideas or suggestions to troubleshoot?

Solution 1:

I solved my problem by unchecking the setting for "GSSAPI key exchange" to work with the Solaris10 hosts I connect to. Answering my own question for future Internet users searching with similar symptoms.

Putty 0.71 changelog includes this:

Support for GSSAPI key exchange: an alternative to the older GSSAPI authentication system [...].

The Putty 0.71 and later apparently use this by default. Disabling this setting on my connections to these Solaris10 servers solves my problems. I guess that these Solaris10 servers are so old that they totally choke when Putty tries this type of key exchange.