Upgrade 5.5.6 to 5.6.4 failing with "Error: null"

[cjohnsonuk]

I'm on 5.5.6
I'm downloading this file: https://www.espocrm.com/downloads/up...6-to-5.6.4.zip
I'm running the upgrade and it says "Error:null" in a red box rather than completing.
Restoring the files from backup fixes it. Rerunning the process results in the same issue.
loading the page after the failed update results in an Server error 500.
ssl_error_log says :
... PHP Catchable fatal error: Argument 1 passed to Espo\\Core\\Container::get() must be an instance of Espo\\Core\\string, string given, called in /var/www/html/crm/application/Espo/Core/Application.php on line 48 and defined in /var/www/html/crm/application/Espo/Core/Container.php on line 41, referer: https://myserver.mydomain.com/crm/index.php

running rebuild.php as suggested in the pinned post results in

PHP Catchable fatal error: Argument 1 passed to Espo\Core\Container::get() must be an instance of Espo\Core\string, string given, called in /var/www/html/crm/application/Espo/Core/Application.php on line 48 and defined in /var/www/html/crm/application/Espo/Core/Container.php on line 41

Permissions and ownership all seem OK.

Any help appreciated

[cjohnsonuk]

Does it now require PHP 7.1? I've still on an earlier version?

[Maximus]

Hello.
Yes. You should use PHP7.1+.

[cjohnsonuk]

PHP upgraded, used the "System requirements" option in admin to check all requirements now met, reran the install and its all fine! :-)
Thanks