Unable to resolve class error , drools 5.5 in concurrent execution. JSR94Support and Spring -------------------------------------------------------------------------------------------- Key: DROOLS-538 URL: https://issues.jboss.org/browse/DROOLS-538 Project: Drools Issue Type: Bug Security Level: Public(Everyone can see) Affects Versions: 5.5.0.Final Environment: Linux Red Hat , Enterprise, JDK 1.6, Drools 5.5.Final Reporter: Maruthi Shanmugam Assignee: Mark Proctor Priority: Blocker 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.