Unable to establish SSL connection (Windows)

this error usually comes up if the protocol versions don't match. For example if your server uses TLS1.2 and the client tries to use TLS1.0. -> This would only work if the server is backwards compatible, otherwise you'll see the message that you posted. Whenever you connect to your server, the software behind it expects the so called 'ServerHello'. It can also happen if the server doesn't support SSL at all.

As you stated, that it's working with Linux, check which Protocol your Windows machine is using. This is also suggested by the ':unknown protocol' string in the message that you posted.

Additional debug options:

• You can try to use wget with the option --no-check-certificate
• Further debugging would be to request the SSL-connection via it's port. You can do this via wget http://>server<:443 -> If this works, you need to enable SSL on the 443 port. Otherwise wget doesn't offer too much debugging information, so you'd need to use something more sophisticated like f.e. the openssl client in combination with it's debug option.

Hope this helps :)