Sorry to see that your question hasn’t received an answer yet. Unfortunately, after this much time, it is unlikely that an answer for this specific question will be provided. For people still landing here via search, the tips provided on WinSCP’s website should help you figure out the issue:

• https://winscp.net/eng/docs/message_unexpected_close

Solution:
You need to change the default password using the Droplet Console (upper right corner) before you can SSH using PuTTy or WinSCP. Once you login with root and default pass it will ask you to change it immediately. (You can paste it with Ctrl+V) Type new password twice and you should be able to SSH with the new password now. That’s what worked for me.