I was not able to update my Oracle database schema.
The reason is a mistake in synax in the script activiti.oracle.upgradestep.6001.to.6002.engine.sql.
Instead of [sql]alter table ACT_RU_EXECUTION add column EVT_SUBSCR_COUNT_ INTEGER;[/sql] it should be [sql]alter table ACT_RU_EXECUTION add ( EVT_SUBSCR_COUNT_ INTEGER );[/sql]