Looks like this is the root problem why task is not created:
10:26:51,222 ERROR [stderr] (Thread-70) java.lang.NullPointerException
10:26:51,223 ERROR [stderr] (Thread-70) at org.jbpm.task.identity.LDAPUserGroupCallbackImpl.existsUser(LDAPUserGroupCallbackImpl.java:134)
10:26:51,224 ERROR [stderr] (Thread-70) at org.jbpm.task.service.TaskServiceSession.doCallbackUserOperation(TaskServiceSession.java:1225)
10:26:51,225 ERROR [stderr] (Thread-70) at org.jbpm.task.service.TaskServiceSession.getTasksOwned(TaskServiceSession.java:763)
10:26:51,225 ERROR [stderr] (Thread-70) at org.jbpm.task.service.TaskServerHandler.messageReceived(TaskServerHandler.java:309)
10:26:51,226 ERROR [stderr] (Thread-70) at org.jbpm.task.service.hornetq.HornetQTaskServerHandler.messageReceived(HornetQTaskServerHandler.java:43)
10:26:51,226 ERROR [stderr] (Thread-70) at org.jbpm.task.service.hornetq.BaseHornetQTaskServer.run(BaseHornetQTaskServer.java:104)
10:26:51,227 ERROR [stderr] (Thread-70) at java.lang.Thread.run(Unknown Source)
I believe LDAP query does not return expected results, please make sure the filter you defined for it in the config file is valid and returns results as expected.
HTH