I am using Drools-core.jar(version-5.0.0.CR1) and getting the following exception. I could see similar stacktrace reported with JIRA-1888(https://jira.jboss.org/jira/browse/JBRULES-1888) and its marked as closed. Fix related to this Jira is not available (Rete.java) in the Drools 5.0.1 and 5.1.0 source code/drools-core jar files. public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException { entryPoints = Collections.synchronizedMap((Map<EntryPoint, EntryPointNode>) in.readObject()); ruleBase = ((DroolsObjectInputStream)in).getRuleBase(); super.readExternal( in ); } java.util.ConcurrentModificationException at java.util.HashMap$HashIterator.nextEntry(HashMap.java:841) at java.util.HashMap$ValueIterator.next(HashMap.java:871) at org.drools.reteoo.ClassObjectTypeConf.getMatchingObjectTypes(ClassObjectTypeConf.java:171) at org.drools.reteoo.ClassObjectTypeConf.getObjectTypeNodes(ClassObjectTypeConf.java:163) at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:143) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:1066) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:1022) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:810) Please let me know the correct fix for this problem. -- View this message in context: http://old.nabble.com/ConcurrentModificationException-during-runtime-at-o... Sent from the drools - user mailing list archive at Nabble.com.