UUID 0X40020056: RPC local-only allocation error fix

Quick answer

Run rpcdump.exe /clear from an admin prompt, then restart the RPC service. If that fails, delete the stale reg key under HKLM\SOFTWARE\Microsoft\Rpc\UuidTemporaryData and reboot.

What's actually happening here

I saw this last week on a client's Domain Controller that had a botched DNS zone transfer. The UUID allocation is a DCOM/RPC thing—Windows assigns a unique identifier for remote calls. When it says "valid only on this local computer," it's telling you the UUID was handed out, but it didn't replicate to any other machines. Usually happens after you change the server's IP or hostname, or when there's a replication conflict between domain controllers. The error code 0X40020056 itself is a warning, not a critical failure, but it'll choke any cross-server RPC calls until you clear it.

Step-by-step fix

1. Open an admin command prompt—right-click Command Prompt, choose Run as administrator. Don't skip this or the clear command won't work.
2. Run RPC dump tool:
   rpcdump.exe /clear
   This clears the local UUID cache. If you don't have rpcdump.exe, grab it from the Windows SDK or use a Sysinternals tool like psrpc.exe.
3. Restart the RPC service:
   net stop RpcSs && net start RpcSs
   Wait 30 seconds. The service will regenerate fresh UUIDs.
4. Verify the fix:
   Run rpcdump.exe with no flags—check that no UUIDs show "LOCAL_ONLY" status. If they're all "OK," you're good.
5. Reboot if it's still broken—sometimes the RPC service hangs onto old state even after restart. A full reboot clears that out.

Alternative fixes if the above doesn't work

• Delete the temporary UUID registry key: Open Regedit, go to HKLM\SOFTWARE\Microsoft\Rpc\UuidTemporaryData. Delete everything under that key. Back up first. Then restart RPC.
• DNS flush: Run ipconfig /flushdns && ipconfig /registerdns. Stale DNS records cause RPC to grab a local-only UUID because it can't resolve the server's own hostname.
• Check for duplicate SPNs: Run setspn -Q */* and look for duplicates. Duplicate SPNs make RPC think it's talking to the wrong machine.
• Last resort: Remove the server from the domain, reboot, rejoin. I've only had to do this once on a badly hosed 2016 server.

Prevention tip

Before you rename a server or change its IP, run rpcdump.exe /clear first. Then change the address. And always let DNS propagate before restarting RPC. Had a client last month whose entire print queue died because they renamed a print server without clearing the UUID cache first—took me an hour to trace the problem.