I’m trying to install a new copy of CiviCRM for Wordpress on Plesk Onyx. I get the following error when I try to activate CiviCRM after uploading the files to my server:

Warning: require_once(CRM/Core/ClassLoader.php): failed to open stream: No such file or directory in /var/www/vhosts/ruinsideca.org/infoportal.ruinsideca.org/wp-content/plugins/civicrm/civicrm.php on line 877

Fatal error: require_once(): Failed opening required 'CRM/Core/ClassLoader.php' (include_path='.:/opt/plesk/php/7.2/share/pear') in /var/www/vhosts/ruinsideca.org/infoportal.ruinsideca.org/wp-content/plugins/civicrm/civicrm.php on line 877

I don’t know why this error is happening or how to fix it. I’ve never come across something like this before. As a result, I can't even install CiviCRM on my server.

I'm running PHP 7.2.22, Wordpress 5.2.3, and CiviCRM 5.17.3.

Thanks for your help

  • Just to make sure, is there a file at /var/www/vhosts/ruinsideca.org/infoportal.ruinsideca.org/wp-content/plugins/civicrm/CRM/Core/ClassLoader.php? Maybe something didn't get fully uploaded. Or maybe the file owner/permissions are wrong?
    – Demerit
    Commented Sep 12, 2019 at 5:56
  • The file exists. I set the permissions to allow everything on that file. It's still not working.
    – com1tech
    Commented Sep 12, 2019 at 19:12
  • @com1tech I suspect the permissions are the problem. Try making Classloader.php permissions 644.
    – Tommy B
    Commented Sep 12, 2019 at 19:54
  • 1
    Thanks everyone for your suggestions. I found that there was a plugin conflict that was causing the issue. After disabling the plugin, I was able to install CiviCRM.
    – com1tech
    Commented Sep 12, 2019 at 23:01
  • 1
    I encountered this also, it was the plugin "CiviCRM integration for Caldera Forms" which I'd installed before CiviCRM and this caused the problem described above. Commented Jan 22, 2020 at 6:10

2 Answers 2


Same happened to me. On installing new test CiviCRM under WordPress. The "CiviCRM Contribution Page Widget" plugin caused same error. Civi 5.27.1, WP 5.4.2, php 7.2.24 on ubuntu 20.04 LTS

  • Is this an Answer or just a 'me too'
    – petednz - fuzion
    Commented Jul 26, 2020 at 20:39

I encountered similar error messages attempting to activate CiviCRM 5.28.0 (but not on Plesk).

The error in that situation was caused by a previous, failed installation attempt on the site this one had been cloned from. Removing all CiviCRM files and tables then enabled the plugin to be activated correctly.

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