RPC_NT_WRONG_ES_VERSION (0XC003005A) Fix Guide

What This Error Means

You're seeing RPC_NT_WRONG_ES_VERSION (0XC003005A) because the Endpoint Serialization Package version on your client machine doesn't match what the server expects. I've seen this most often when connecting a Windows 10 machine (20H2 or later) to an older Windows Server 2012 R2 or 2016 box, or after a botched Windows Update that left files halfway updated.

I know getting an obscure hex error instead of a clear message is frustrating. Let's fix it step by step.

Fix 1: Reboot the Client and Server (30 seconds)

This sounds too simple, but I've seen it work more times than I'd like to admit. The serialization package can get stuck in a bad state after a partial update or a hung session.

1. Restart the client machine (the one showing the error).
2. Restart the server (the one it's trying to connect to).
3. Try the operation again.

If that didn't help, move on to Fix 2.

Fix 2: Restart the RPC Endpoint Mapper Service (5 minutes)

The RPC Endpoint Mapper service (RpcEptMapper) manages the serialization package registrations. A simple restart can reload the correct version.

1. Press Win + R, type services.msc, hit Enter.
2. Scroll to Remote Procedure Call (RPC) Endpoint Mapper.
3. Right-click it, choose Restart.
4. Also restart this service on the server if you have access.
5. Reboot both machines again (yes, it matters—the restart resets the cache).

If the error persists, move to Fix 3.

Fix 3: Re-register the RPC Proxy DLL (5 minutes)

The serialization package relies on rpcproxy.dll. A corrupt or missing registration can trigger version mismatches. Here's how to re-register it.

1. Open an elevated Command Prompt (right-click Start > Command Prompt (Admin) or PowerShell as Admin).
2. Run these two commands in order:

   regsvr32 /u rpcproxy.dll
   regsvr32 rpcproxy.dll

3. You'll see success messages for both.
4. Reboot the machine.

I've fixed this on both Windows 10 and Server 2019 with that step. Still broken? Let's go deeper.

Fix 4: Check and Fix Registry Version Keys (15+ minutes)

This is the advanced fix. The serialization package version is stored in the registry under HKLM\SOFTWARE\Microsoft\Rpc. If the version numbers got mangled (common after a failed Windows Update rollback), you need to set them straight.

Warning: Editing the registry can break things if you're not careful. Back it up first (File > Export in regedit).

1. Open regedit (Win + R, type regedit, hit Enter).
2. Navigate to:

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc

3. Look for a key called SerializationPackageVersion. If it's missing, you'll need to create it:
   • Right-click the Rpc key, choose New > DWORD (32-bit) Value.
   • Name it SerializationPackageVersion.
4. Double-click that DWORD. For Windows 10 20H2 and later, set the value to 5 (decimal). For Windows Server 2016, use 4. For Windows Server 2012 R2, use 3.
5. Click OK, close regedit, and reboot.

If you're not sure which version your server expects, check the server's registry at the same path. Match the client's value to the server's. That's the real fix—it forces both to use the same serialization version.

When All Else Fails

I've seen cases where a Windows Update itself caused the mismatch, specifically KB5006670 (November 2021 patch) on older builds. If the registry fix didn't work:

• Uninstall the most recent Windows Update (Settings > Update & Security > View update history > Uninstall updates).
• Or do an in-place upgrade repair using the Windows Media Creation Tool—it replaces the RPC subsystem cleanly.

You should be back in business. Drop me a comment on the blog if you hit a wall—I've fixed this dozens of times, and I'll help you through it.