Having just purchased the admin manual I've found the section on "scoping classes using ears" and have created a jboss-app.xml file as specified. However this has not resolved the problem. I am presuming that this file should be included within the meta-inf direction of the ear file. Is this correct?
You need to make sure the entity beans from the EAR gets bound to different global names if you deploy it twice (by default both will try to use the same ejb-name if you don't override it). See the jboss.xml DTD (/docs/dtd) and how to use the <jndi-name> element.