[WiX-users] Error 1648 Installing Patch

[JWalker <imp...@ya...>]

Hi,
I have a patch built using the WiX-only approach. I can view it in Orca with the original MSI, and everything looks good. But when I go to apply the patch, the installer displays the message "No valid sequence could be found for the set of patches". The values are all correct in the MsiPathSequence table (patch family "TestPatchFamily", sequence "1.0.0.1", the product code, and attributes "0"). Does anyone have any idea what could be causing this error? Here is an excerpt from the log:
MSI (c) (DC:C4) [13:11:50:579]: Validating transform 'RTM.1' with validation bits 0x922
MSI (c) (DC:C4) [13:11:50:579]: Transform 'RTM.1' is valid.
MSI (c) (DC:C4) [13:11:50:579]: PATCH SEQUENCER: QFE patch E:\Installer\Patches\TestPatch.msp is applicable.
MSI (c) (DC:C4)
 [13:11:50:579]: PATCH SEQUENCE ERROR: E:\Installer\Patches\TestPatch.msp patch is missing sequencing info!
MSI (c) (DC:C4) [13:11:50:579]: SequencePatches returns error 1648.
No valid sequence could be found for the set of patches.

I don't know whether this might be a factor, but we do some post-processing of the heat-generated .wxs files to put each component in its own fragment. The MSI file installs fine... Many Thanks!