Failed to install WordPress in Plesk for Windows: Task is not responding

Symptoms

• Upon the attempt to install WordPress, the following error is displayed in Plesk interface:

  PLESK_ERROR: Failed to install WordPress. Task is not responding: id=6618, pid=3188, type=ext-wp-toolkit-task\install

• The following error is displayed in %plesk_dir%admin\logs\php_error.log :

  CONFIG_TEXT: [2017-12-07 18:51:34] DEBUG [extension/wp-toolkit] Current task progress is 100.
  [2017-12-07 18:51:34] ERR [1] ERROR: Cannot redeclare class AddendioConfigHelper (AddendioConfigHelper.php:6). [2017-12-07 18:51:38] ERR [panel] Task is not responding: id=6603, pid=3188, type=ext-wp-toolkit-task\install.

• Addendio extension is installed;

Cause

Unclear

Resolution

1. Log into Plesk

2. Remove the Addendio extension via Plesk > Extensions > Addendio > Remove .