SOLUTION:
The agent.jar was in the lib folder. The lib folder was on classpath.
I repaced the agent.jar. This solved the issue.

Thanks a lot.

Thanks for this wonderfull question !
Unlimited custom actions can be added on "Configuration > User Defined Metric Actions” page.

Here is a tutorial about adding custom actions for your reference: http://www.wlsdm.com/tutorials/advanced-weblogic-monitoring-develop-jmx-mbeans-and-automate-with-wlsdm-metric-actions.php