Select the process and click on tasks (URL http://localhost:8080/jbpm-console/app/procdef.jsf?id=1&view=task)

The result is an exception
Error loading task list: An exception of type "org.hibernate.exception.DataException" was thrown. The message is: could not execute query

From log
Error loading task list: An exception of type "org.hibernate.exception.DataException" was thrown. The message is: could not execute query

Will reproduce with higher log level