Upgrading Drupal

Сообщение об ошибке
Notice: Array to string conversion in Drupal\Component\Render\HtmlEscapedText->__construct() (line 37 of core/lib/Drupal/Component/Render/HtmlEscapedText.php).

I have a site with about 5000 pages in two languages. The site has books and in D6 the book navigation block displayed only those books that were relevant for the specific language

So in English the Book Block would display

Sections:

• Book 1
• Book 2
• Book 3
• Book 4

and in French the Book Block would display

Sections:

• Livre 1
• Livre 2
• Livre 3

Having migrated to D7 what I get is all the book pages displaying the Book block:

Sections:

I updated from 7.42 to 7.43 and ran the update, but I cannot get to any of my administrative areas like reports or Configuration. I get errors like the following:

Not Found

The requested URL /admin/structure was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I am logged in. I'm totally lost on this one. I was able to go in and get site out of maintenance mode via a direct link, but that is about it.
What do I do???

I'm trying to upgrade from 7.26 to 7.43 but after following the instructions here, /update.php returns a blank page.

When I visit the site homepage, I receive the following error...

Hi everyone,

If I build my website with Drupal 8, will it be easily to upgrade my website from Drupal 8 to Drupal 9 (when it releases) without rebuilding a new website?

Thanks and best regards,

I've been working hard on upgrading our drupal 6 site to drupal 7. Have been following steps in upgrade.txt; and am working on my second practice site. With core at 6.38 and all my contrib modules updated, when I run update.php, with the latest 7.x core I get this error: