You get this error when you try to run a remote command or connect to a server using RPC. For example, you might see it when you run net use to map a drive, or when a management tool like Server Manager tries to talk to another server. I've seen it most often after a Windows Update patch Tuesday, or when someone disabled a service to "improve security."
The full error usually looks like this: RPC_S_CANNOT_SUPPORT (0x000006E4) - The requested operation is not supported.
What's causing this?
The root cause is almost always one of two things:
- The RPC service itself isn't running. This happens when someone set it to Manual or Disabled. The RPC service needs to be running at all times on a Windows Server.
- The RPC Endpoint Mapper (RpcEptMapper) service is off. This service listens for remote requests. Without it, RPC calls get rejected.
Less common causes: a firewall blocking port 135 (RPC Endpoint Mapper), or a corrupt registry key. But start with the services — that fixes 9 out of 10 cases.
Step-by-step fix
Step 1: Open Services
Press Win + R, type services.msc, and hit Enter. This opens the Services window.
Step 2: Check the RPC service
Find Remote Procedure Call (RPC) in the list. Look at the "Status" column. If it says "Running", good. If it's blank, right-click it and select Start.
Then look at the "Startup Type" column. It should say Automatic. If it doesn't, right-click the service, pick Properties, and set it to Automatic from the dropdown. Click Apply, then OK.
After this, you should see the status change to "Running" within a few seconds.
Step 3: Check the RPC Endpoint Mapper
Find RPC Endpoint Mapper (sometimes called DCOM Server Process Launcher). Same check: it must be both Running and Automatic. If not, right-click it, choose Start, and set its startup type to Automatic in Properties.
Step 4: Reboot the server
Once you've fixed both services, restart the server. This makes sure all dependent services pick up the changes. After the reboot, try your original command again.
What if it still fails?
If the error comes back, check these three things:
- Firewall: Make sure port 135 (TCP) is open on both the local and remote server. Use
telnetfrom a command prompt to test. If telnet fails, add a firewall rule to allow RPC traffic.135 - Event Viewer: Open Event Viewer (Win + R, type
eventvwr.msc). Go to Windows Logs > System, and look for error events related to RPC or DCOM. They often have a clue like "DCOM got error 0x800706E4" which is the same thing. - Group Policy: If this is a domain member, check Group Policy settings under Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options. Look for "Network access: Named Pipes that can be accessed anonymously" and make sure it includes
EPMAPPER. Missing that can block RPC.
One more thing: I've seen this error on Windows Server 2019 after the KB5005573 update. In that case, uninstalling the update fixed it until Microsoft released a patch. If the services are fine and the firewall is open, check your recent updates and consider removing the latest one.
That usually nails it. Good luck.