I had same error over RDP. Problem is to set ignore certificates and use NLA authentication (windows 2012 R2) This settings helped me connect with success:
<connection name="Windows"> <protocol>rdp</protocol> 192.168.0.2 3389 test password nla true true </connection> -- Sent from: http://apache-guacamole-general-user-mailing-list.2363388.n4.nabble.com/
