Comment 5 for bug 683249

In my case there was a certificate validation error because of the tunneling: the certificate was issue for <hostname> and not <localhost> so the connection was refused. On the advanced tab I had to change the Security from Negotiate to RDP or TLS and then it worked.
I also had to delete my known_hosts file in .freerdp because of an offending key. I only learnt about this when I started remmina from commandline.