After installing the latest version of CiviCRM (5.56.1) I cannot open my website anymore and log is showing this message:

Got error 'PHP message: Uncaught PHP Exception Exception: "Serialization of 'Closure' is not allowed" at /data/sites/web/instituutvlaamsevolkskunstbe/cms-install/4466-instituut-voor-vlaamse-volkskunst/production/vendor/civicrm/civicrm-core/CRM/Extension/ClassLoader.php line 85'

and drush cr returns:

Serialization of 'Closure' is not allowed

Drupal version 9.5.0 PHP version 7.4.33

I cannot find anything related

Thanks, Stefaan


1 Answer 1


Composer 2.5.1, just released, fixed this. Run composer self-update, then composer install on the site to update the class loader.

Composer 2.5 is not compatible with civi, yet. Use composer self-update --rollback for now; then run composer install again on your site.


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