Forum Discussion

zbevdp's avatar
zbevdp
Copper Contributor
Dec 19, 2025

AOVPN / Reasoncode 16

We have an always on vpn configuration.  This worked fine till few months ago, users can't get connected anymore. After reboot of NPS server, all works fine for some time (random, sometimes 1 day, 2 ...
AOVPN
nps
VPN
windows server
Jamony's avatar
Jamony
MCT
Sep 17, 2026

NPS Reason Code 16 is reported when authentication fails because the supplied credentials don't match the user account. Microsoft recommends checking the username/account state and which DC handled the request.

 

However, because you're using PEAP/EAP-TLS, I would also inspect the certificate side. Capture the complete Event 6273 when the failure occurs and check the certificate subject/SAN, EKU, chain, expiration and mapping to the AD user/computer.

 

Also check the DC logs for certificate-mapping events related to KB5014754. If a reboot temporarily fixes the issue but it returns and occurs on a replacement NPS server as well, I would investigate shared dependencies such as AD/DC communication, CRL/AIA availability and certificate mapping rather than the NPS installation itself.