Wrong forum. Use the users' forum for this. And before posting please read this post:
Furthermore: You told us you are using jBPM 4.2 but your process definition references the 4.0-schema. Please check if you are not mixing up things.
Modify the schema of the process to 4.2, which is what I'm using but the error persists
take a look at the tomcat server log. there should be an explanation.