I fixed the errors by adding the following jars to jbpm-human-task-war.war
dom4j-1.6.1.jar
hibernate-annotations-3.4.0.GA.jar
hibernate-commons-annotations-3.1.0.GA.jar
hibernate-core-3.3.2.GA.jar
hibernate-entitymanager-3.4.0.GA.jar
hibernate-jpa-2.0-api-1.0.1.Final.jar
hornetq-core-2.2.10.Final.jar
javassist-3.14.0-GA.jar
and by changing entity-mappings version from 2.0 to 1.0
HTH
Laura