you should consider replacing toplink essentials with EclipseLink (on GFv2.1 we got best results with EclipseLink 1.0.2).
Toplink Essentials is flawed and IMO unusable.
Just place the eclipselink.jar in the /lib subdirectory of your domain, and then put the following line in your domain.xml:
<system-property name="com.sun.persistence.defaultProvider" value="org.eclipse.persistence.jpa.PersistenceProvider"/>
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