I have have two test apps: one fails, the other works ok. Each persists a simple class to a simple db2 table.

For the app that fails, comparing the log4j log to the app that runs ok, it looks like the SessionFactoryObjectFactory fails to initialize, ie I do not see the 'initializing class SessionFactoryObjectFactory' message in the log (for the app that fails). Following this I get the following exception:
net.sf.hibernate.MappingException: could not instantiate id generator

What would cause this? As far as I can tell the hibernate.cfg.xml files for both apps are identical (apart from pointing to different mapping files), and the mapping files themselves are similar in structure (although using different classes and mapping to different classes.

Any ideas where I can start looking?

Thanks,
Kevin Hooke

Check your <generator class="..."/> line in the broken one. It probably sucks.

Got it.. thanks