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UCEERR_UNKNOWNPACKET
UCEERR_UNKNOWNPACKET is a Windows User Composition Engine (UCE) HRESULT. It indicates that the rendering channel received a packet type that the active composition engine does not recognize.
What to check for UCEERR_UNKNOWNPACKET
- Check component and runtime version compatibility across the application and installed.NET or Windows updates.
- Look for custom interop, injected graphics components, or corrupted composition-channel traffic.
- Record the full exception stack and Windows build before attempting a retry.
Microsoft guidance for WPF render-thread failures
Diagnostic interpretation
This result has the HRESULT value 0x88980401. AllStat records the condition as “it”.
Evidence to capture
- Capture any IErrorInfo text, activity identifier, event-log entry, and subsystem trace that mentions this result or the uceerr / unknownpacket operation.
- Reproduce this result with the smallest valid input and note whether the result changes with identity, architecture, service state, or target object.
Retry and recovery
Retry this result only when the owning API documents a transient state or after the condition described as “it” has changed.
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