Hi Jean,
The use of events and event handlers can be customized in your case. You may try the following steps to achieve what you want -
1.Have customized error message at a point where you want to stop or after the check which upon failure the test should be stopped.
2.Enable events
3.From general events, select onLogError event and add event handler/listner to it.
4.In event handler/listener function check for the customized message if posted in the logs. If that is found in logs stop the test by Runner.Stop() else come out of function.
I have used this method in my tests and it works.
-Amit