Hi , We use Drools 5.5 and drool implementation is done through Spring JSR94Support API> The Rule engine is called in concurrent mode, i.e , JSR94Support.executeStateless(name,list) is executed through multiple threads. And when the rules are executed we randomly get the following exception org.drools.RuntimeDroolsException: Unable to resolve class 'someclass(this is sample)here actual class is printed>' at org.drools.base.ClassFieldAccessorCache.getClass(ClassFieldAccessorCache.java:126) at org.drools.base.ClassFieldAccessorCache.getClassObjectType(ClassFieldAccessorCache.java:48) at org.drools.reteoo.ClassObjectTypeConf.<init>(ClassObjectTypeConf.java:83) at org.drools.common.ObjectTypeConfigurationRegistry.getObjectTypeConf(ObjectTypeConfigurationRegistry.java:71) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:159) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:903) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:847) at org.drools.reteoo.ReteooStatelessSession.executeWithResults(ReteooStatelessSession.java:273) The rules are registered every 15 minutes through RuleAdministrator.registerRuleExecutionset , so whenever we refresh the rules and the subsequent thread even after the registration is completed, fails with the above message. This happens only when the rules are invoked concurrently. Please advise. -- View this message in context: http://drools.46999.n3.nabble.com/Unable-to-resolve-class-error-drools-5-... Sent from the Drools: User forum mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users