I have similar problem with a jbossas 5.1
Even when at start-up tje server says it has bound the jndi name, in the administration console the datasource is down.
When trying to deploy a single ejb-jar with the administration console the follwing error id thrown
Deployment "vfszip:/usr/local/java/jboss/jboss-5.1.0.GA/server/test-field/deploy/lunch-ejb-1.0.0-SNAPSHOT.jar/" is in error due to the following reason(s): java.lang.RuntimeException: mapped-name is required for lunchDS of deployment EmployeeService
the same error is thrown if the ejb-jar is already in the deploy folder at start-up http://jbossas.pastebin.com/MZ5M9qgT