Fix RPC_NT_UNSUPPORTED_NAME_SYNTAX (0xC0020026) in Windows

When This Error Hits

You're trying to connect to a remote server using PowerShell Remoting, or maybe you're running an RPC call from a C# app, and boom — you get the error RPC_NT_UNSUPPORTED_NAME_SYNTAX (0xC0020026). The exact message says "The name syntax is not supported."

I see this most often when someone tries to use a UNC path like \\server\share inside an RPC API call — especially with functions like RpcStringBindingCompose or RpcBindingFromStringBinding. It also happens with WinRM when you pass a computer name in the wrong format, like using a UUID string instead of a DNS name.

What's Really Happening

RPC uses different "name syntax" types. The most common is RPC_C_NS_SYNTAX_DEFAULT (value 0), but sometimes you get RPC_C_NS_SYNTAX_DCE (value 3) or something else. When you pass a string that doesn't match the expected syntax, RPC says "I don't understand this format" and throws error 0xC0020026.

Think of it like this: you're speaking English, but the RPC service expects Spanish. The words might be correct, but the structure is wrong.

The Fix: 3 Steps

Step 1: Check the name format

For most Windows RPC calls, you want to use the DNS format. For example:

Correct: server01.contoso.com
Wrong:  {server01} or server01/ or \\server01

If you're using a UUID in the string binding, make sure it's in the standard format:

Correct: objectUUID=12345678-1234-1234-1234-123456789abc
Wrong:   12345678-1234-1234-1234-123456789abc (missing "objectUUID=")

Step 2: Set the syntax explicitly (if needed)

If you're writing code, explicitly set the syntax when calling RpcStringBindingCompose or RpcBindingFromStringBinding. Don't rely on defaults. Here's a C++ example:

RPC_WSTR StringBinding;
RPC_STATUS status = RpcStringBindingCompose(
    NULL,                              // Object UUID (optional)
    (RPC_WSTR)L"ncacn_ip_tcp",        // Protocol sequence
    (RPC_WSTR)L"server01.contoso.com", // Network address (DNS format)
    (RPC_WSTR)L"1234",                // Endpoint
    NULL,                              // Options
    &StringBinding);

if (status != RPC_S_OK) {
    // Handle error — likely 0xC0020026 if name syntax is wrong
}

Step 3: Test with a different protocol

Sometimes the error is protocol-specific. If you're using ncacn_np (named pipes), switch to ncacn_ip_tcp for testing. Named pipes need a different name format (like \\server\pipe\name) that can trigger this error if you pass it to the wrong function.

If It Still Fails

Check the string binding more carefully. Common gotchas:

• You used a comma instead of a colon in the endpoint (like 1234, instead of 1234)
• The object UUID has a typo or wrong case — RPC is case-sensitive here
• You passed a GUID with braces {} around it — RPC doesn't want those
• The protocol sequence name is wrong (like ncacn_ip_tcp misspelled as ncacn_it_tcp)

I've tripped over this error myself more times than I'd like. Usually it's something dumb like a missing colon or a stray backslash. Compare your string against Microsoft's example in the RPC String Binding documentation — it's saved me hours.