every time singleton session manager is created it stores ksession id as serialized file in temporary/data location. See here for details. Depending how you run the code it can be stored in different locations:
- when running on JBoss it will be in JBOSS_HOME/standalone/data
- otherwise it will be in java.io.tmpdir directory
- alternatively you can provide custom location using jbpm.data.dir system property
This error (warning) is harmless as it simply indicates it found serialized file but there is no session in data base so it creates new one, no side effects.