Customize message of OFBiz

[hoandv]

Hi all
I have this below script:
<eca service="A" event="commit" >
    <action mode="sync" service="B"/>
</eca>
when service B is failed, I want to expose a message like "myMessage". But
screen displays:

Error calling event: org.ofbiz.webapp.event.EventHandlerException: Service
invocation error (Could not commit transaction for service [A] call: Roll
back error, could not commit transaction, was rolled back instead because
of: Error in simple-method [B]:  + "myMessage"

Can you show me how to customize message of OFBiz  so that it  displays
 only "myMessage" on screen .
Thank all