I just posted this to another topic regarding the same thing...
I'm guessing this is because for the EJB 3.0 install, GA uses Quartz for scheduling. That's just a guess since I never used the JBoss scheduler, only Quartz.
I am having this exact same issue. I assume I am missing a JAR file. Does anyone have any additional information?
Look for scheduler-plugin.jar in the lib directory.
The example for the scheduler is called scheduler-plugin-example.jar