> Now the questions:
> ==================
> Can you think of a situation where a isc_db_handle instance is
> invalid (db.out == null)?
> Could it be a synchronization problem in JBoss or Jaybird?

It, most likely, happens when server reports an error that is considered to
be "fatal" from the point of view of the driver. This invalidates current
connection and opens a new one. However, it seems that the transaction
handle is not marked as invalid and is later used by some connection. At
that point NPE happens.

Roman