Finally the update was a breeze the last week...
FWIW, these "workarounds" didn't work for me:
- Updating to 8.1 via Store.
- Updating through 8.1 ISO disc.
- Making active the boot partition (created by an old W7 installation and used by W8, I think).
- Disabling every single 3rd party services and apps, even uninstalling all of them altogether.
- Cleaning faulty registry entries.
- Deleting the small System partition and making a single partition that holds everything (system, boot, dumps, etc).
- Clean boot.
- etc, etc, etc
None of the above things worked (because I tried hard to keep all my applications untouched while updating)
The following "workaround" was the trick to update:
-Refreshing Windows 8 from its ISO disc (and consequently losing all my programs and apps) prior to update to 8.1 through the Store.
As someone said out there, it seems that 8.1 needs to see a perfectly clean 8.0 boot files which appears always gets messed after "months of use" (no matter how careful you are with maintenance). And that's why my friends that got their systems just updated
to 8.0, no one of them got errors while updating...
Hope it helps :)