Protocol error occurred. Error was returned from the destination server.
The Softether server by default to run on port 443, if you server also hosts normal https then 443 is already taken and so Softether can't bind to it.When you run `vpncmd` it attempts to connect, find an active port, but of course fails with 'Protocol error occurred. Error was returned from the destination server.' because it's not actually connecting to the vpn server.
By default Softether also listens on 992, 1194, and 5555 so the sollution is to modify specify `localhost:5555` when executing the `vpncmnd`. If this has helped you feel free to comment or follow me on twitter @danielsokolows.