On Windows7, using SourceTree 1.6.20 I cannot connect to the remote server over SSH. Fetch, pull, etc. fail. Neither OpenSSH nor Putty/Plink in the Client SSH Configuration works. (Everything is fine with Git from the command line).
With OpenSSh, the CMD prompt for my passphrase opens and closes immediately, without any chance to actually enter the passphrase (This used to work on my old machine with the same key pair).
With Putty/Plink, I'm presented with a server SSH fingerprint which I cannot accept (as it is only in the "Show Full Output" dialog which is not interactive).
Running Plink directly on the command line offers a different fingerprint, so accepting this has no effect on the SourceTree behavior.