ClassNotFoundException BAMTaskSummaryImpl after migration to BPM Suite 6.0.3

Issue

After migrating from BPM Suite 6.0.2 to BPM Suite 6.0.3 following exception is displayed in the log during startup:

Caused by: java.lang.ClassNotFoundException: org.jbpm.services.task.impl.model.BAMTaskSummaryImpl from [Module "org.hibernate:main" from local module loader @7d95609 (finder: local module finder @4d9f6ce5 (roots: C:\Tools\jboss-eap-6.1\modules,C:\Tools\jboss-eap-6.1\modules\system\layers\bpms,C:\Tools\jboss-eap-6.1\modules\system\layers\base))]
    at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:196) [jboss-modules.jar:1.2.2.Final-redhat-1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:444) [jboss-modules.jar:1.2.2.Final-redhat-1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:432) [jboss-modules.jar:1.2.2.Final-redhat-1]
    at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:374) [jboss-modules.jar:1.2.2.Final-redhat-1]
    at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:119) [jboss-modules.jar:1.2.2.Final-redhat-1]
    at java.lang.Class.forName0(Native Method) [rt.jar:1.7.0_67]
    at java.lang.Class.forName(Class.java:270) [rt.jar:1.7.0_67]
    at org.hibernate.internal.util.ReflectHelper.classForName(ReflectHelper.java:170)
    at org.hibernate.ejb.Ejb3Configuration.classForName(Ejb3Configuration.java:1333)
    at org.hibernate.ejb.Ejb3Configuration.addNamedAnnotatedClasses(Ejb3Configuration.java:1405)
    ... 11 more

What is the reason for this and how to fix it?