I also use firmware 6.1.3.4
I had check the NPS event log, error message is " There is no domain controller available for domain OP002." Event code: 4402.
I had source around this event code at microsoft website but it said is because NPS server can't the domain controller or windows firewall.
But, my deployment is domain controller, DNS, DHCP, NPS all are in same server. But we have two domain controller, and just configure 1 NPS only on 1 of the domain controller.