Windows 10: WIN10 upgrade 1511 to 1607 fails. Error 0dx000009a

I have installed WIN10 (ver. 1511) a couple of months ago. While trying to solve a driver issue I've been advised (by MICROSOFT) to upgrade to ver.1607. Several upgrade attempts all failed (with code 0xd000009a) What does it mean? Any more details needed? How can I resolve this? Can't find any clue on the net for this code.

:)

 

Cannot Duplicate displays after Windows 10 upgrade

After upgrading from Win10 1511 to Win10 1607, our computers are not duplicating the display anymore. In our school we have 4000PCs and fortunately most of them are Win10 1511. Please fix the issue, so we can upgrade to 1607.

 

Dell Vostro 1520 failed rollback from Windows 10 to Windows 7, infinite reboot loop

If you upgraded to Win10 "months ago," it's too late to rollback to Win7.

If you upgraded from Win10 1511 to Win10 1607, going back to your previous build would take you back to Win10 1511.

 

For the past 4 days I've been trying to find a way to identify why my Anniv. Update fails. There does not seem to be a way to do this.

 

Latest development:
Reading different installation problems on the internet I realized I had the AVAST antivirus ON all the time. After disabling it I tried to upgrade. The process went indeed a few steps further but then came the RESTART stage which failed ! The reason: "bootmgr missing"! The only way to overcome this is by using "recovery drive". If you did not prepare one beforehand you need another computer to do that, which is annoying when you ars in distress... So take the advice and "Be prepared"!
Anyhow, using a recovery drive (details on request) I managed to get my computer running again. As you recall: I was in the middle of upgrading from ver.1511. The process seemed to continue but checking the version revealed that nothing has changed. Well, I did not give up and after a fresh attempt (No.7 or so...) (from within the "WIN10 GREETING and NEWS screen") I managed to finally upgrade to ver.1607 or "Anniversary version".
Thank you all for reading this saga.
Drive carefully....