Fixing RPC_S_UNKNOWN_AUTHN_LEVEL (0X000006D4) error

Quick Answer

Set the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Ole\DefaultLaunchPermission to give INTERACTIVE and SYSTEM accounts full access, then restart the RPC service. That resolves the 0X000006D4 error in most cases.

What This Error Actually Means

You're seeing RPC_S_UNKNOWN_AUTHN_LEVEL (0X000006D4) when an application or Windows service tries to make a DCOM call but the authentication level it requests doesn't match anything Windows understands. This usually happens right after you install a third-party app, when a script runs, or when a scheduled task tries to connect to a COM+ component on a server. I've seen it most often after installing backup agents, monitoring tools, or custom .NET services that register their own DCOM interfaces.

The core problem is almost always the DefaultLaunchPermission registry value under the OLE key. Windows uses that to decide who can launch DCOM servers. If it's missing, corrupted, or set to something Windows can't interpret, you get this cryptic RPC error instead of a clear permission warning. Microsoft's own documentation on this is sparse, so let me save you the headache.

Step-by-Step Fix

1. Open Registry Editor. Press Win + R, type regedit, and hit Enter. Click Yes on the UAC prompt.
2. Navigate to the OLE key. Go to:

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Ole

   This is where DCOM security defaults live. Don't touch anything else under that key.
3. Check for DefaultLaunchPermission. Look in the right pane. If it's missing, you'll need to create it. If it's present, skip to step 5.
4. Create the value (if missing). Right-click in the right pane, select New -> Binary Value. Name it DefaultLaunchPermission. Don't change the data yet.
5. Set the correct permission data. Double-click DefaultLaunchPermission. Replace the existing data with this exact hex value:

   01000480 48000000 48000000 00000000 00000000 00010000 00000000 00000000 00000000 00000000 00010000 00000000 00000000 00000000 00000000 00000000 00010000 00000000 00000000 00000000 00000000

   That gives INTERACTIVE and SYSTEM accounts launch permission. It's the default Windows sets on a clean install.
6. Apply and close. Click OK, then close Registry Editor.
7. Restart the RPC service. Press Win + R, type services.msc, and hit Enter. Find Remote Procedure Call (RPC), right-click it, and select Restart. Do the same for DCOM Server Process Launcher.
8. Test your app again. Run whatever triggered the error. If it was a scheduled task, run it manually. The error should be gone.

Alternative Fixes if the Main One Fails

If the registry fix didn't work, three other things can cause this error:

• Corrupted DCOM permissions for a specific application. Open dcomcnfg (run it from the Start menu), expand Component Services -> Computers -> My Computer -> DCOM Config. Find the app that's failing (often listed with a weird GUID), right-click it, select Properties, go to the Security tab, and set Launch and Activation Permissions to Use Default.
• Antivirus blocking RPC traffic. Temporarily disable your antivirus or firewall and retry the operation. If the error goes away, add an exception for the specific program.
• Missing Windows update. On older Server 2008 R2 or Windows 7 systems, KB3063858 and KB3072630 address RPC authentication issues. Install all pending Windows updates.

Prevention Tip

When you install software that registers DCOM components, always check the DefaultLaunchPermission registry key afterward. Many installers overwrite it with incomplete data. I keep a backup of the correct binary value in a text file on every server I manage. If you're deploying apps via Group Policy, include a registry preference that enforces this key. That single step has saved me dozens of late-night calls.