Upgrading Drupal

I suffer (!) from the error:

Source database does not contain a recognizable Drupal version.

It happens when I try to upgrade a working all-fine Drupal 7 site to a fresh Drupal 8 site with the module "Migrate update" (or in its other name "Drupal Upgrade").

I've detailed everything here. Please also read the comments:

I offer answer-acceptence, thumbs up, and 150reputation bounty for a working answer.

I am totally new to Drupal. I have no knowledge of php but have been tasked with maintaining a website.
I am getting an error in the home page of my website as shown below. The site is working fine but that error comes up right in the users' faces when they visit the site and complaints are flowing in. The error reads as-

Notice: Undefined index: za8cbc054 in include() (line 1 of /hermes/walnaweb01a/b2966/pow.bneadmin/htdocs/drupal/sites/all/themes/business/templates/page--front.tpl.php)

I've been hoping upgrading my D6 sites would be easy, but I'm already lost from the start. If I understand correctly, I'm not supposed to install D8 on my sites' servers. But where do I have to arrange the fresh D8 installation then? I'm not a hardcore programmer, and most of you probably will consider me to be a noob not knowing what to do, but I hounestly don't understand how to go through the steps as explained.

In investigating a migration from a Drupal 7 site to a Drupal 8 site I've run into a show stopper that I don't know enough about to solve. One of my most important content types I've called "Twain Sites". In the D7 site this type has fields for "Title", URL redirect, URL path settings, "Body", "Geo Field" (Latitude and longitude), "Node Reference" (Select List with multiple values), "Marker Category" (select list with a single value), "Which Book" (select list with multiple values, "Site Image" (multiple images), and "Site Document" (multiple files).

Bonjour,

Je suis en train de penser à la migration de mes sites en drupal 6 et je découvre Drush.
Oter moi un doute.
On peut vraiment faire toutes ces actions sur un site à distance dans se connecter ?
Cela me parait inquitant, mais je ne vois personne parler de se connecter sur les tutos que je découvre.

Bonne année 2016
EM

Hello,

Hi and happy new year,

I am stuck with a D6 to D7 migration.. so I'll add one more post to the endless number of migration laments...

My fresh D7 site is set up with all the necessary content types and fields, ready to relieve the migration.
One thing I did not get : do I have to rebuild my Views before the migration?