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TPC_E_UNKNOWN_PROPERTY
Meaning and numerical form
TPC_E_UNKNOWN_PROPERTY is HRESULT 2147746331 (0x8004021B; signed -2147220965). AllStat records its meaning as “TabletPC inking error code. Unknown property specified”. In practical terms, it is returned when Tablet PC code receives a property identifier that is not recognized by the relevant ink, packet or recognition component.
The severity bit in 0x8004021B is set, so this result is a failure result rather than a success or informational status. Its facility is 4 (FACILITY_ITF) and its low 16-bit code is 539 (0x021B). Those fields classify the value but do not identify the component instance, call, object or input that produced it.
Where the failure belongs
This result belongs to Tablet PC ink, stylus and recognition. Tablet PC APIs span device enumeration, RealTimeStylus packet queues, ink-object lifetime and recognizer-specific capabilities. The numerical facility does not identify which Tablet PC layer produced the result. The decisive condition is this: Tablet PC code receives a property identifier that is not recognized by the relevant ink, packet or recognition component. Record the first native producer instead of relying only on a framework exception translated several layers later.
Do not infer from this result alone that reinstalling, rebooting or repeating the whole workflow is appropriate. Because it can cross process and language boundaries, its correction depends on the object identity, lifecycle generation, input and state at the first failing call.
Diagnostic sequence
- Capture this result at the first native return and identify the exact object and method.
- Confirm that the observed path matches this condition: Tablet PC code receives a property identifier that is not recognized by the relevant ink, packet or recognition component.
- compare the live state with the method contract before changing configuration.
- collect the code-specific evidence listed above and preserve any more specific preceding error.
- change one evidence-backed cause at a time, then repeat the smallest operation that can prove the correction.
- Add a regression check that distinguishes it from the related outcomes described below.
Likely causes
- Possible cause 1 for this HRESULT: a GUID is misspelled or belongs to another property family.
- Possible cause 2 for this HRESULT: a custom property was not registered or carried with the ink data.
- Possible cause 3 for this HRESULT: the installed platform version does not know the requested property.
Evidence to collect
A useful it record includes the native API or interface method, component or CLSID, process and thread IDs, architecture, apartment where relevant, operation correlation ID, elapsed time, input identity, and the first state-changing event before failure. When diagnosing it, preserve IErrorInfo, an inner HRESULT, Win32 status, device event or provider message when available.
- Capture 1 for this HRESULT: property GUID, expected value type and owning interface.
- Capture 2 for this HRESULT: list of properties actually present or supported.
- Capture 3 for this HRESULT: serialized ink or packet schema version.
Telemetry for this HRESULT should retain types, lengths, hashes, stable opaque identifiers and lifecycle generations while redacting content and credentials. This makes repeated incidents comparable without exposing ink content, packet data, account details or recognizer input.
Correction and retry boundary
- Corrective action 1 for this HRESULT: query supported properties before reading optional values.
- Corrective action 2 for this HRESULT: preserve custom-property registration and serialization metadata.
- Corrective action 3 for this HRESULT: treat unknown optional properties as extensibility rather than corrupting the entire object.
Retry guidance for this HRESULT. Retry only after choosing a supported property or installing the component that defines it. A retry must avoid this hazard: replay stale strokes, reorder stylus packets or reuse an invalid recognizer context. It must also preserve the evidence needed to locate the original producer of it.
Practical scenario
A plug-in asks RealTimeStylus for a recognizer-only property GUID; enumerating packet properties first prevents it. The result scenario narrows the result to a reproducible contract boundary and supplies a concrete before-and-after test.
Developer and operational guidance
Code handling it should log the failed stage before cleanup, keep ownership and lifecycle transitions explicit, and avoid converting every failure into a generic message. Tests for this HRESULT should cover the primary cause, one adjacent HRESULT and the retry boundary so a future change cannot turn a deterministic contract failure into an uncontrolled loop.
Operational repair for this HRESULT should use supported device, Tablet PC component, recognizer and application lifecycle paths. Avoid unsupported configuration edits or component replacement unless evidence identifies that layer. Retain the original trace and a post-fix trace so the result can be attributed and the change reversed.
Difference from nearby HRESULTs
TPC_E_INVALID_PROPERTY often means a known property is unavailable or unsupported in a recognizer context; it means the identifier itself is unknown to the component. Keep these outcomes separate in logs, exception mappings, user messages, dashboards and automated retry policy.
Official Microsoft references
- Microsoft: generic COM error codes
- Microsoft: Tablet PC property GUIDs
- Microsoft: IRealTimeStylus::SetDesiredPacketDescription
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