This is probably an EJB3 question, as this exception should be expected in either case.
Make a copy of the object, using a copy-constructor or whatever, then persist the copy to the other entity manager.
I cloned my object. But I still get the same exception.
Now if I made my entity non caching, then it works fine. This is the code I use to make my entities cacheable.
I think you'll have better luck getting an answer on the Hibernate forums at hibernate.org. This seems to be more a question about how Hibernate deals with entities when a 2nd level cache is configured, rather than about the details of JBC.
Thanks Brian. I will try that.