After doing other tests: updating the process definition and restarting my application (web application using seam and jbpm) a found an other similar Exception:
java.lang.RuntimeException: Unable to load session snapshot
at org.drools.persistence.SessionMarshallingHelper.loadSnapshot(SessionMarshallingHelper.java:96)
at org.drools.persistence.SingleSessionCommandService.initKsession(SingleSessionCommandService.java:238)
at org.drools.persistence.SingleSessionCommandService.<init>(SingleSessionCommandService.java:191)
…...
Caused by: java.io.EOFException
at java.io.DataInputStream.readShort(DataInputStream.java:298)
at java.io.ObjectInputStream$BlockDataInputStream.readShort(ObjectInputStream.java:2751)
at java.io.ObjectInputStream.readShort(ObjectInputStream.java:927)
at org.jbpm.marshalling.impl.ProcessMarshallerImpl.readProcessTimers(ProcessMarshallerImpl.java:204)
at org.drools.marshalling.impl.InputMarshaller.readSession(InputMarshaller.java:310)
at org.drools.marshalling.impl.InputMarshaller.readSession(InputMarshaller.java:196)
at org.drools.marshalling.impl.DefaultMarshaller.unmarshall(DefaultMarshaller.java:93)
at org.drools.persistence.SessionMarshallingHelper.loadSnapshot(SessionMarshallingHelper.java:91)