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ERROR_UNKNOWN_PATCH
Patch identity is separate from the MSP filename
ERROR_UNKNOWN_PATCH (1647) is returned when an operation targets a patch registration that Windows Installer cannot find for the product. Patches have PatchCode GUIDs, and an MSP file can be renamed without changing that internal identity.
The patch may never have been applied, may have been superseded or removed, may belong to another product context, or the caller may have supplied a ProductCode/PatchCode pair that was never associated. Seeing an MSP in a download or cache directory does not prove it is registered for a product.
Evidence to collect
- Extract the PatchCode from the exact MSP rather than deriving it from the filename.
- Enumerate patches registered for the target ProductCode and user/machine context.
- Check whether a later patch superseded or obsoleted the requested patch.
- Distinguish cached patch media from applied-patch registration.
- Verify that management inventory has not retained a stale patch GUID.
- For removal, confirm that the patch is individually uninstallable before invoking uninstall.
References
- Microsoft: patch packages
- Microsoft: extracting patch information as XML
- Microsoft: removing patches
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