Hi,
what does return following query on your data base:
select
propertyim0_.KEY_ as KEY1_6_,
propertyim0_.VERSION_ as VERSION2_6_,
propertyim0_.VALUE_ as VALUE3_6_
from
JBPM4_PROPERTY propertyim0_
It should return two rows, one for db.version and second for next.dbid.
If you don't have it I would recommend to drop your jbpm schema and create it once again. Please use ant tasks for that that are delivered with jBPM distribution.
drop.jbpm.schema -Ddatabase=postgresql
create.jbpm.schema -Ddatabase=postgresql
create.jbpm.schema task will insert all required items into that table.
HTH
Maciej