We run into issue related to the <jar-file> setting in persistent.xml when we deploy it in jboss server 5.1.0.GA. It is not a issue when we deploy it in jboss 4.2.2.GA.
Here is the detail. We need to include some other entities from different jar file. What we do is to include it using <jar-file>, like the following:
/lib/another.jar myejb.jar ....