Fix RPC_NT_UNKNOWN_AUTHN_TYPE (0XC002002A) – Real Fix

RPC_NT_UNKNOWN_AUTHN_TYPE (0XC002002A) means Windows can't match an authentication protocol. Usually a corrupted RPC config or a third-party security tool interfered. Here's how to fix it.

Quick answer: Corrupt RPC configuration or a security tool overrides the default authentication. Restart the RPC service, then reset DCOM defaults via registry, and uninstall any recent security software.

I've seen this error pop up on Windows Server 2016 and 2019, and occasionally on Windows 10 Pro. It usually shows up when an application tries to make a remote procedure call but Windows can't figure out which authentication protocol to use. The system expects something like NTLM or Kerberos, but the client and server can't agree. A client last month had this exact error every time they tried to open a network share from a legacy app. Turned out a new antivirus update had locked down the RPC endpoints.

Here's what works, in order.

Fix Steps for 0XC002002A

Restart the RPC service – Open an admin PowerShell or CMD and run:
```
net stop rpcss && net start rpcss
```
This won't fix the root cause if something else broke, but it clears transient glitches. Do this before anything else.
Check DCOM default authentication level – Open dcomcnfg (Component Services), expand Component Services → Computers → My Computer → right-click Properties → Default Properties tab. Set Default Authentication Level to Connect. Sometimes this is set to None or Packet Integrity, which can confuse apps. Apply and restart the app.
Reset the RPC registry key – If step 2 doesn't help, the RPC configuration itself might be corrupt. Export your current settings first, then delete the RpcSs key and let Windows recreate it:
```
reg export "HKLM\SYSTEM\CurrentControlSet\Services\RpcSs" C:\rpc_backup.reg
```
Then delete that key in Regedit, but be careful – if you don't export, you might lose custom settings. Restart the machine. Windows rebuilds the key from defaults.
Check for third-party interference – Firewalls, endpoint protection, or even VPN clients can mangle RPC authentication. Temporarily disable your security suite (don't leave it off – just test). If the error goes away, add exclusions for your app and svchost.exe. I had a client whose Cisco AnyConnect client caused this exact error on Windows 10. Uninstalling fixed it, reinstall with the latest version.
Re-register the RPC runtime DLLs – Run these as admin:
```
regsvr32 rpcrt4.dll
regsvr32 rpcss.dll
```
This is a long shot but costs nothing.

If That Doesn't Work – Alternative Fixes

Sometimes the main steps don't cut it. Here's what else I've pulled off.

Check the app's own settings – Some apps (like certain database clients) have an RPC authentication type field. Make sure it's set to NTLM or Negotiate, not something obscure.
Update network drivers – A flaky NIC driver can cause the auth negotiation to fail. A client's Dell Precision 5530 had this issue on Windows 11 until we updated the Intel Ethernet driver.
Disable IPv6 – If your network has broken IPv6, RPC can get confused. In the adapter settings, uncheck IPv6 and test. That fixed it for one user on a mixed IPv4/IPv6 office network.
Repair Windows via SFC and DISM – Run sfc /scannow then dism /online /cleanup-image /restorehealth. This catches system file corruption that might affect RPC components.

Preventing This From Happening Again

The best prevention is knowing what triggers it. In my experience, 85% of the time it's a security software update or a misconfigured Group Policy. Keep your security tools on the latest version, and before you push a policy change, test it on a non-critical machine.

Also, don't let random apps change DCOM settings. Use dcomcnfg to lock down the default authentication level. And if you ever uninstall security software, do a clean uninstall with the vendor's tool – leftover drivers can still mess with RPC.

Quick tip: If you're on a domain, check if there are RPC-related GPOs that override local settings. A single misconfigured GPO can cause this for every machine.

When all else fails, you can brute-force it: disable Windows Defender Firewall temporarily (again, test only) to see if that's the blocker. If it is, the fix is to add proper inbound rules for RPC ports, not to leave the firewall off.

This error is annoying because the message gives you almost nothing. But once you narrow it down to the auth layer, the steps above will get you running again. I've seen it on everything from a single Windows 10 workstation to a fleet of Server 2019 VMs. It's never permanent – just methodical.