I am getting the exact same error using the default db hypersonic. This occurs during my long running test that I have setup to send 10 million messages from 3 different JMS clients. The test is set up to send batches of 1000 messages and sleep for 10 seconds. The messages are received by a message driven bean and a log message is created for every 1000 messages recieved. I am not performing any other business logic. After about 2 million messages, I get a NullPointer exception on the server side and a unique constraint violation on the client side.
Any ideas here?