I'm trying to upgrade a friend's website from 5.7.4.1 to 8.5.1 and also upgrade to PHP7. The site is fairly simple with a dozen pages and a dozen blog posts.

From what I saw online, I need to update to 5.7.5.13 first before updating to 8.x. Making that intermediate upgrade is not working because the site returns an error message - Cannot access protected property Concrete\Core\Page\Page::$vObj - on both the public side and the admin side.

I don't have much experience with concrete5. I'm testing the upgrade process on a website clone on a subdomain rather than the live website.

Steps to make website clone
- copied files from live site to subdomain directory
- copied database from live site to new database
- modified (subdomain)/application/config/database.php to use new database
- in Config table, deleted marketplace.token and marketplace.url_token records

(Website appears in browser as expected and I'm able to log in. All steps below were in C5 Dashboard for the subdomain)

- disabled caching and cleared cache
- uninstalled all packages (HTML5 Audio Player Basic - 2.0.4 and Open Graph Tags Lite - 2.0.2) and moved the packages to trash directory on server
- connected the subdomain website to the Community (and it's visible in my C5 account)

(so far, so good--navigation works, SSL works, C5 Dashboard works.)

Steps to upgrade C5
- downloaded 5.7.5.13 from C5 repository
- extracted files and copied only the concrete folder to subdomain directory, replacing the old folder
- deleted (subdomain)/application/config/update.php
- loaded (subdomain)/index.php/ccm/system/upgrade in the browser where I was logged in as administrator--Upgrade concrete5 window appears, showing the correct upgrade
- upgrade process completes

But the upgrade process does not succeed--clicking on the "Back to Home" button or loading the cloned website in a different browser both produce the same error message:
An unexpected error occurred.
Cannot access protected property Concrete\Core\Page\Page::$vObj"

But I can still see the C5 Dashboard and navigate through the different sections there. I just can't go to any pages.

When I tried the next step of upgrading to 8.5.1 (by copying the concrete folder to the subdomain home directory), I lost access to the dashboard with the error message:

Whoops \ Exception \ ErrorException (E_RECOVERABLE_ERROR)
Argument 2 passed to Concrete\Core\Page\Single::createPageInTree() must implement interface Concrete\Core\Site\Tree\TreeInterface, null given, called in /home/(subdomain folder)/concrete/src/Backup/ContentImporter/Importer/Routine/ImportSinglePageStructureRoutine.php on line 42 and defined

I made backups of the database and files before attempting the upgrade, so I can revert to that.

What should I try next?

Is it possible to upgrade directly from 5.7.4.1 to 8.5.1?

Thanks,
Tim