# File lib/openid/server.rb, line 383
      def answer_unsupported(message, preferred_association_type=nil,
                             preferred_session_type=nil)
        if @message.is_openid1()
          raise ProtocolError.new(@message)
        end

        response = OpenIDResponse.new(self)
        response.fields.set_arg(OPENID_NS, 'error_code', 'unsupported-type')
        response.fields.set_arg(OPENID_NS, 'error', message)

        if preferred_association_type
          response.fields.set_arg(
              OPENID_NS, 'assoc_type', preferred_association_type)
        end

        if preferred_session_type
          response.fields.set_arg(
              OPENID_NS, 'session_type', preferred_session_type)
        end

        return response
      end