I did plenty of XenDesktop 7.x upgrades but this time I got error 0x643 when trying to update the Citrix StoreFront components.
StoreFront 3.5 –> StoreFront 3.9
Installation of ‘..\CitrixStoreFront-x64.msi’ failed with error code 1603. Fatal error during installation.
Solution: The customer was using the Citrix SCOM Management Pack. After killing the processes called “ComTrade.MPxxxx.exe” the upgrade was succesfull.