Hi MM,
The DatabaseIdGenerator need second commandService to fetch the id from database in a seperated Transaction, please refer jbpm.default.cfg.xml
<object class='org.jbpm.pvm.internal.id.DatabaseDbidGenerator'>
<field name="commandService"><ref object="newTxRequiredCommandService" /></field>
</object>
I didn't know anything about the third commandService, maybe it is an out of date configuration.