Can you connect, if you downgrade? Can you connect using any other client using the same protocol? Don't you have a firewall with per-application rules, which may check an executable file checksum? (what would explain the problem happening after upgrade)

WinScp has been connecting no problems everyday. Today i updated it and now it won't connect! No real indication why. Just says connection failed. No information has changed and is all pre-entered. any ideas?