onFormProcessed problem

I'm trying to add custom processing for a form. Created a plugin and registrered for the onFormProcessed event as per the manual. But when submitting the form it fails with an error stating that the event received must be an instance of Grav\Plugin\Event but that the event it got was RocketTheme\Toolbox\Event\Event.
Grateful for any suggestion on how to fix this.

You need to add the appropriate use statement to specify the Event class:

<?php
namespace Grav\Plugin;

use RocketTheme\Toolbox\Event\Event;
...

Thank you! Problem solved.