Fix RPC_S_UNKNOWN_AUTHZ_SERVICE (0X000006D6)

A 30-Second Fix That Usually Works

Before you do anything else, restart the Remote Procedure Call (RPC) service. I've seen this error pop up on Windows 10, Server 2016, and Server 2019 when the service gets stuck after an update or a network hiccup. Here's how:

1. Press Win + R, type services.msc, and hit Enter.
2. Scroll down to Remote Procedure Call (RPC). It should be running. If it's not, right-click it and choose Start.
3. Also check DCOM Server Process Launcher right above it. That one must be running too.
4. After starting both, try whatever triggered the error again — a remote admin tool, a backup job, or a scheduled script.

Expected outcome: If the service was stopped, the error should disappear immediately. If it's already running, this won't help — move to the next fix.

The 5-Minute Fix: Registry Tweaks

The real culprit behind 0X000006D6 is often a missing or corrupted registry entry for the Authentication Service. The error translates to "the authorization service is unknown," which means Windows can't find the right GUID for the security package it needs. Here's how to check and fix it.

Step 1: Check the AuthService Registry Key

1. Press Win + R, type regedit, and hit Enter. Click Yes if UAC asks.
2. Navigate to this exact path:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa

3. Look for a value named AuthService. If it doesn't exist, you'll need to create it.

Step 2: Create or Fix the AuthService Value

Right-click on an empty space in the right pane, choose New > DWORD (32-bit) Value, and name it AuthService. Double-click it and set the value data to 1 (this tells Windows to use the default authentication package). Click OK.

Expected outcome: After closing regedit, restart the RPC service again (or reboot if you're on a production server you can restart). The error should stop showing up. If it persists, there's one more thing to try.

The 15-Minute Fix: Re-Register Authentication DLLs

Sometimes the registry is fine but the actual DLLs that handle authentication got corrupted or unregistered — this happens after a botched Windows update or security tool interference.

1. Open Command Prompt as Administrator. Right-click the Start button and pick Command Prompt (Admin) or Windows PowerShell (Admin).
2. Run these two commands, one at a time. Press Enter after each.

regsvr32 /u /s schannel.dll
regsvr32 /s schannel.dll

3. Now do the same for the NTLM security package:

regsvr32 /u /s wdigest.dll
regsvr32 /s wdigest.dll

4. Finally, restart the RPC service one more time. Right-click Remote Procedure Call (RPC) in services.msc and choose Restart.

Expected outcome: The commands should return silently — no success message is normal. After the restart, test your remote call again. I've seen this fix work when the registry tweak didn't, especially on Windows Server 2012 R2 and 2016.

When None of This Works

If you're still seeing 0X000006D6, the problem might be bigger. Check these:

• Corrupted system files: Run sfc /scannow from an admin command prompt. Let it finish — it takes about 15 minutes.
• Group Policy: A domain policy might be blocking the authentication service. Check Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options for anything related to Network security: Restrict NTLM.
• Third-party software: Antivirus or firewall software can block RPC traffic. Temporarily disable them to test. If the error goes away, add an exception for RPC (port 135 and dynamic RPC ports).

I've personally seen this error happen on a Windows 10 machine that had McAfee Endpoint Security installed — the firewall module was killing RPC calls. Disabling it fixed it immediately.