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RPC_S_UNKNOWN_IF
Interface registration is local runtime state
RPC_S_UNKNOWN_IF means the RPC runtime does not recognize the interface in the context of the requested operation. Server applications register each supported interface with RpcServerRegisterIf or a related function. Management and lookup operations that refer to an interface can fail when that registration is absent.
The error is more specific than a network failure. It often occurs entirely inside the server process before any endpoint or transport problem is relevant.
What to compare
- Verify that the same MIDL-generated interface specification handle is passed to registration, endpoint publication, and inquiry calls.
- Check interface UUID and major/minor version, especially when client and server were generated from different IDL revisions.
- Review shutdown and reload ordering so the interface is not unregistered while endpoint or object management code still uses it.
When diagnosing a live server, enumerate registered interface IDs rather than assuming that a successful service start implies every interface registered successfully.
References
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