java.lang.NullPointerException
at org.drools.common.ConcurrentNodeMemories.getNodeMemory(ConcurrentNodeMemories.java:63)
at org.drools.common.AbstractWorkingMemory.getNodeMemory(AbstractWorkingMemory.java:1034)
at org.drools.rule.SlidingTimeWindow$BehaviorExpireWMAction.<init>(SlidingTimeWindow.java:460)
This is not a new problem, I found an old post on the mailing list, that describes the same here: (but unfortunately without any answers)