Error: "8506,421" repeatedly appears on Asus Transformer Windows 8.1

Error: "8506,421" appears repeatedly on my ASUS Transformer T100T with Windows 8.1.  I am using the latest Norton 360 multidevice program, with all updates Norton tells me are due. 

This does not happen all the time; it seems to be about once every few weeks.  I uninstall and reinstall and then the problem goes away - for a while.  At the same time, and all the time,  all the Windows updates fail, even though the update and restart screens show the updates have been installed, which can take several hours.  However, Windows Update then shows all updates failed.  I have disconnected the USB mouse and my VPN connection; same problem reoccurs.  I also have Malwarebytes free version.

Any suggestions would be most welcome.