Fix windows failed to install the following update with error 0x80070643 - Windows 10 Tips And Tricks | Windows101Tricks | Scoop.it
From www.windows101tricks.com - September 9, 2016 8:25 AM

“Unable to install Windows Update: 0x80070643”. This error message can be seen when the .NET framework on your computer has problem,
or the update related to MS 2003 components fails. if your PC is running Windows 10 and you tried to apply KB3122947 update you might also see the same error code “Update for Windows 10 Version
1511 for x64-based Systems (KB3122947) - Error 0x80070643” Here are some tips to fix this