What does HRESULT 0x800C000D (INET_E_UNKNOWN_PROTOCOL) mean?

 
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INET_E_UNKNOWN_PROTOCOL

INET_E_UNKNOWN_PROTOCOL is a URL Moniker HRESULT. It means that no protocol handler recognized the URL scheme or the requested scheme is not supported in the current Windows configuration.

What to check for INET_E_UNKNOWN_PROTOCOL

  • Validate the URL scheme and make sure it is spelled correctly and registered for the intended handler.
  • Use a protocol supported by the application and its deployment environment.
  • Investigate handler registration or policy restrictions if a normally supported scheme is unavailable.

Microsoft documentation

Diagnostic interpretation of INET_E_UNKNOWN_PROTOCOL

INET_E_UNKNOWN_PROTOCOL has the HRESULT value 0x800C000D. AllStat records the condition as “The specified protocol is unknown.”. For INET_E_UNKNOWN_PROTOCOL, in practice, interpret that wording at the boundary owned by the Windows component or COM interface that returned the HRESULT, rather than treating the value as a generic Windows message.

Evidence to capture for INET_E_UNKNOWN_PROTOCOL

  • Record the exact COM method or Windows API, its input object, the calling thread, and the full 0x800C000D value before a wrapper converts it to an exception or Boolean result.
  • Capture any IErrorInfo text, activity identifier, event-log entry, and subsystem trace that mentions INET_E_UNKNOWN_PROTOCOL or the inet / unknown / protocol operation.
  • For INET_E_UNKNOWN_PROTOCOL, compare the failing machine with a working one at the same configuration boundary: component version, policy, registration, identity, and target resource.

Retry and recovery for INET_E_UNKNOWN_PROTOCOL

Retry INET_E_UNKNOWN_PROTOCOL only when the owning API documents a transient state or after the condition described as “The specified protocol is unknown.” has changed. For INET_E_UNKNOWN_PROTOCOL, configuration, policy, format, and authorization failures normally require correction first; an immediate loop can hide the original call site and add secondary errors.

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