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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 discriminator: Capture the packet type at the composition-channel boundary. This status means the active UCE endpoint does not recognize that packet type, which differs from transport unavailability or queue overload.
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