[rules-users] session deserialization slidingTimeWindow NPE

Sometimes (I am not sure what the actual reason is yet ) I get following NPE when I try to deserialize my ksessions: 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) http://drools.46999.n3.nabble.com/rules-users-5-5-0-Final-persistence-to-... Apparently it's got something to do with slidingTime in one rule, but as it does not always occur - am I quite puzzled. Any Ideas or Workarounds? - Alex