Operations with WordPress instance fail in Plesk WP Toolkit: Call to undefined function

Symptoms

Operations with WordPress instance fail in Plesk WP Toolkit:

Failed to reset cache for the instance #568: PHP Fatal error: Uncaught Error: Class 'QodeStartitFramework' not found in /var/www/vhosts/example.com/httpdocs/wp-content/plugins/pluginname

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PHP Warning: Undefined array key "SERVER_NAME" in /var/www/vhosts/example.com/httpdocs/wp-content/plugins/plugin_name/...
...
Error: Call to undefined function create_function()

Cause

Corrupted WordPress plugin.

Resolution

1. Log in to Plesk.

2. Disable the WordPress plugin mentioned in the error message.

   Note: If the corrupted WordPress plugin is required, try to reinstall it. If reinstallation does not help, contact plugin vendor to get further support.