Hello, I experienced some problem while working on IBM WebSphere 7.0.0.3 (64 bit) and IBM JVM V9 (1.6.0) with Drools 5.0.1. To be precise, I get NPE from inside java.util.concurrent.CopyOnWriteArrayList object. The problem repeats randomly and I didn't detect an exact factor that causes it. For me, it looks like an issue in JVM, but I'd like to know if anyone here experienced it. KnowledgeBase has been deserialized from DroolsObjectInputStream before creating session. The exact stack trace goes here: 2009-09-03 17:14:46,487 [SimpleAsyncTaskExecutor-2] ERROR amg.exion.statements.StatementContentManager - Exception thrown while generating marketing info: java.lang.NullPointerException at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:273) at java.util.concurrent.CopyOnWriteArrayList.add(CopyOnWriteArrayList.java:393) at org.drools.event.AbstractEventSupport.addEventListener(AbstractEventSupport.java:52) at org.drools.common.AbstractRuleBase.addEventListener(AbstractRuleBase.java:846) at org.drools.reteoo.ReteooRuleBase.newStatefulSession(ReteooRuleBase.java:332) at org.drools.reteoo.ReteooRuleBase.newStatefulSession(ReteooRuleBase.java:306) at org.drools.impl.KnowledgeBaseImpl.newStatefulKnowledgeSession(KnowledgeBaseImpl.java:151) at org.drools.impl.KnowledgeBaseImpl.newStatefulKnowledgeSession(KnowledgeBaseImpl.java:134) at amg.exion.statements.internal.processor.impl.DroolsSessionGenericProcessorImpl.process(DroolsSessionGenericProcessorImpl.java:54) at amg.exion.statements.internal.processor.impl.DroolsSessionStatementProcessorImpl.processStatement(DroolsSessionStatementProcessorImpl.java:72) at amg.exion.statements.StatementContentManager.process(StatementContentManager.java:272) at amg.exion.statements.StatementContentManager.process(StatementContentManager.java:80) at org.springframework.batch.core.step.item.SimpleChunkProcessor.doProcess(SimpleChunkProcessor.java:118) at org.springframework.batch.core.step.item.SimpleChunkProcessor.transform(SimpleChunkProcessor.java:260) at org.springframework.batch.core.step.item.SimpleChunkProcessor.process(SimpleChunkProcessor.java:171) at org.springframework.batch.core.step.item.ChunkOrientedTasklet.execute(ChunkOrientedTasklet.java:70) at org.springframework.batch.core.step.tasklet.TaskletStep$2.doInChunkContext(TaskletStep.java:268) at org.springframework.batch.core.scope.context.StepContextRepeatCallback.doInIteration(StepContextRepeatCallback.java:81) at org.springframework.batch.repeat.support.RepeatTemplate.getNextResult(RepeatTemplate.java:367) at org.springframework.batch.repeat.support.RepeatTemplate.executeInternal(RepeatTemplate.java:215) at org.springframework.batch.repeat.support.RepeatTemplate.iterate(RepeatTemplate.java:143) at org.springframework.batch.core.step.tasklet.TaskletStep.doExecute(TaskletStep.java:242) at org.springframework.batch.core.step.AbstractStep.execute(AbstractStep.java:198) at org.springframework.batch.core.job.AbstractJob.handleStep(AbstractJob.java:348) at org.springframework.batch.core.job.flow.FlowJob.access$0(FlowJob.java:1) at org.springframework.batch.core.job.flow.FlowJob$JobFlowExecutor.executeStep(FlowJob.java:135) at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:60) at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:144) at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:124) at org.springframework.batch.core.job.flow.FlowJob.doExecute(FlowJob.java:103) at org.springframework.batch.core.job.AbstractJob.execute(AbstractJob.java:250) at org.springframework.batch.core.launch.support.SimpleJobLauncher$1.run(SimpleJobLauncher.java:110) at org.springframework.core.task.SyncTaskExecutor.execute(SyncTaskExecutor.java:49) at org.springframework.batch.core.launch.support.SimpleJobLauncher.run(SimpleJobLauncher.java:105) at amg.exion.statements.internal.StatementsInternalImpl$1.run(StatementsInternalImpl.java:100) at java.lang.Thread.run(Thread.java:735) Best regards, -- Przemysław Różycki IT Architect AMG.net, A Bull Group Company ul. Łąkowa 29 90-554 Łódź, Poland www.amg.net.pl