Hi, I am using Drools Kbase stateful sessions and using "changeset.xml" file to dynamically load resources (DRL files) from a folder. The KnowledgeAgent configuration property 'drools.agent.newInstance' is set to false. And the 'drools.resource.scanner.interval' property is set to 1. As I am using Spring, these properties are passed-in to the agent from spring-beans.xml. Now, when I start tomcat, everything works fine (some rules also get fired), But when I remove a DRL rule from my resource folder following exception is thrown: Exception in thread "Thread-8" java.lang.NullPointerException at org.drools.reteoo.RuleTerminalNode$RTNCleanupAdapter.cleanUp(RuleTerminalNode.java:507) at org.drools.reteoo.BetaNode.doRemove(BetaNode.java:253) at org.drools.common.BaseNode.remove(BaseNode.java:109) at org.drools.reteoo.RuleTerminalNode.doRemove(RuleTerminalNode.java:411) at org.drools.common.BaseNode.remove(BaseNode.java:109) at org.drools.reteoo.ReteooBuilder.removeRule(ReteooBuilder.java:237) at org.drools.reteoo.ReteooRuleBase.removeRule(ReteooRuleBase.java:432) at org.drools.common.AbstractRuleBase.removeRule(AbstractRuleBase.java:831) at org.drools.common.AbstractRuleBase.removeRule(AbstractRuleBase.java:809) at org.drools.impl.KnowledgeBaseImpl.removeRule(KnowledgeBaseImpl.java:206) at org.drools.agent.impl.KnowledgeAgentImpl.removeKnowledgeDefinitionFromBase(KnowledgeAgentImpl.java:842) at org.drools.agent.impl.KnowledgeAgentImpl.incrementalBuildResources(KnowledgeAgentImpl.java:763) at org.drools.agent.impl.KnowledgeAgentImpl.buildKnowledgeBase(KnowledgeAgentImpl.java:586) at org.drools.agent.impl.KnowledgeAgentImpl.applyChangeSet(KnowledgeAgentImpl.java:185) at org.drools.agent.impl.KnowledgeAgentImpl$ChangeSetNotificationDetector.run(KnowledgeAgentImpl.java:1106) at java.lang.Thread.run(Thread.java:662) Is there anything more that needs to be set for 'changeset' to work for add/update/remove of resources? FYI - I am using Drools 5.1.1 Thanks, Prashant -- View this message in context: http://drools.46999.n3.nabble.com/Removing-rule-DRL-from-resource-throwin... Sent from the Drools: User forum mailing list archive at Nabble.com.