There is probably a jdbc driver conflict on your hsqldb database. Make sure to use the correct database jar.
I copied the hsqldb.jar that comes with jbpm-starters-kit to the default/lib folder of my JBoss instance. So, I think I am using the same version of hsqldb.jar; but I still get the same error.
you need JBPM database schema created in the hsqldb database. run jbpm-db\hsqldb\upgrade.scripts\hsqldb.create.jbpm.3.1.sql if you will. and you need to deploy the websale process also. by running "ant deploy.processes -buildfile build.deploy.xml" under jbpm/