When you comment out @PersistenceContext, you stop making your entity anything but a regular java class. With @PersistenceContext in place, the classes marked as entities may become "weaved" in memory, which means that their bytecode is sometimes modified to support JPA features that the JPA provider chose to implement that way.
If you don't define a persistence unit on the client, you might need to have your entities statically weaved to be matched between the client and the container.
Regards,
-marina
[Message sent by forum member 'mvatkina' (mvatkina)]
http://forums.java.net/jive/thread.jspa?messageID=293136