Four hours of swearing at servers, kicking switches and rebooting printers and terminals and all because of a Windows Update.

Our entire network uses 802.1X authentication with certificates and this morning I arrived in the office to find all the Teradici terminals and network printers were failing to authenticate properly.

We hadn’t changed anything in the NPS policies so has a certificate expired? The errors in the event logs were constant

Event ID 36887 – A fatal alert was received from the remote endpoint. The TLS protocol defined fatal alert code is 42.

And seeing things like:

Network Policy Server denied access to a user.

Contact the Network Policy Server administrator for more information.

    Security ID:            DOMAIN\TERADICI
    Account Name:           teradici@domain.local
    Account Domain:         DOMAIN
    Fully Qualified Account Name:   domain.local/Users/TERADICI

Client Machine:
    Security ID:            NULL SID
    Account Name:           -
    Fully Qualified Account Name:   -
    OS-Version:         -
    Called Station Identifier:      -
    Calling Station Identifier:     5C-F6-DC-11-77-EE

    NAS IPv4 Address:
    NAS IPv6 Address:       -
    NAS Identifier:         -
    NAS Port-Type:          Ethernet
    NAS Port:           1026

RADIUS Client:
    Client Friendly Name:       WORKS Switch-1
    Client IP Address:

Authentication Details:
    Connection Request Policy Name: 802.1x Wired Proxy
    Network Policy Name:        Teradici
    Authentication Provider:        Windows
    Authentication Server:      DC1.domain.local
    Authentication Type:        EAP
    EAP Type:           Microsoft: Smart Card or other certificate
    Account Session Identifier:     -
    Logging Results:            Accounting information was written to the local log file.
    Reason Code:            16
    Reason:             Authentication failed due to a user credentials mismatch. Either the user name provided does not map to an existing user account or the password was incorrect.

Now because the event log filled up with 1,000’s of SChannel errors it only went back to 9:00am as it had rolled off the older messages. So looking at the IAS log files I discovered the problem started at around 3:47am. A look at the event viewer Setup log I noticed that 3 Windows Updates had been applied. Amongst them KB4034681 – which after a Goggle returned the article that states:

Know Issues in this Update

NPS authentication may break, and wireless clients may fail to connect.

Bingo. Add in the Workaround and printers immediately logged in, terminals restarted their connection and all was at peace with the world again.

On the server, set the following DWORD registry key’s value to = 0: