Hi,
I am not sure it should be xerces - at least it is not part of jBPM distribution.
I would suggest to create your class path strictly based on following libraries:
- ${jbpm43.home}/jbpm.jar
- ${jbpm43.home}/*.jar
Of course you could add your own classes as well but please be careful with adding any xml parsers.
Cheers,
Maciej