Run the database script <EI<BPS_HOME>/wso2/business-process/dbscripts/bps/bpmn/create/activiti.<DB_Name>.create.substitute.sql against your BPMN engine's database to add the Substitution related table.
Open the activiti.xml file found in the <EI<BPS_HOME>/wso2/business-processrepository/conf/ directory and uncomment the following configuration.