Upgrade error

Attempted to upgrade to version 8. The site is now inaccessible with the following error: "An unexpected error occurred.Class \Concrete\Core\Permission\Key\CategoryTreeNodeKey does not exist." At this point I would be satisfied to return to the earlier version. A restore of the site was unsuccessful, with the error remaining and no access.

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MrKDilkington replied on at Permalink Reply
Hi taber,

What versions of concrete5 did you upgrade from and upgrade to?

How did you perform the upgrade?

When you attempted to restore your site, did you restore both your files and database?
taber replied on at Permalink Reply
The site is tabermuseum.org.

The upgrade was from the version 5 (the latest I believe) to version 8. The upgrade was attempted by clicking on the link on the opening splash screen, which I believe led me to the dashboard.

The restoration from the backup was done by 1and1.com, the hosting company and I do not know if the database was restored. It occurred to me that may be the problem when the restoration was unsuccessful.
MrKDilkington replied on at Permalink Reply

The website you are referring to loads correctly.

Before attempting another upgrade, make sure to take a full backup (database and files). Since you had an issue upgrading, I suggest creating a copy of the site and testing the upgrade on the copy.
taber replied on at Permalink Reply
Thanks for your help. The hosting company restored the database too and that solved the problem.