Just an FYI, it appears IncrementGenerator was broken in 2.1.7 as it always quotes the table name. With Oracle, Postgresql, andMySQL, quoting a table name forces case-sensitivity. If your table is named "orders", then MySQL won't find "ORDERS" (that's the name in the SQL printed out).
I've noticed this change has already been rolled back in CVS...just waiting on the next Hibernate release to get this fix.
The change was an attempt to fix
HB-1315 but I think it backfired. I'm still trying to figure out exactly what the problem was. The only I could see when debugging it was that if you specify a quoted identifier for a table name in your hbm file, the IncrementGenerator doesn't seem to pick it up. That might be the actual bug there.