I got the same problem. From google I found this topic, but without solution.
but ,but finally
I solved it by removing the "username" and "password" in the config file of hibernate(hibernate.cfg.xml)
And I changed the generator type from "increment" to "identity".(My id type is "integer", not big-decimal, my db is derby)
this is my case, I think it may be helpful, so....
Not good English, sorry