What does Windows error code 1750 (RPC_S_UNKNOWN_AUTHZ_SERVICE) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: The RPC binding specifies an authorization service identifier that the runtime does not recognize.

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RPC_S_INVALID_AUTH_IDENTITY	EPT_S_INVALID_ENTRY

RPC_S_UNKNOWN_AUTHZ_SERVICE

Authorization service is not the same field as authentication service

RPC_S_UNKNOWN_AUTHZ_SERVICE means the authorization-service value on an RPC security configuration is unknown. RPC APIs such as RpcBindingSetAuthInfoEx accept separate values for authentication service, authentication level, and authorization service.

Because the constants are integers, configuration layers sometimes accidentally place an RPC_C_AUTHN_* value into the authorization field or treat every security identifier as one shared enum. That can produce this status before any credentials are validated.

What to check

Log the symbolic AuthzSvr value alongside AuthnSvc and AuthnLevel.
Use only documented RPC_C_AUTHZ_* constants for the authorization-service parameter.
Review wrapper APIs and serialized configuration for field-order mistakes after structure or version changes.
Do not diagnose Kerberos, NTLM, or certificate failures until the RPC runtime accepts the authorization-service selector.

The fix is local configuration correctness. An endpoint mapper or server restart cannot make an unknown authorization-service identifier valid.

References

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