(I'll try and create a simpler demo, but here's the original.) when Token( $elem: element ) // element is a MaSigType application object AnyTrainSignal( x25no == $elem ) // x25 is an int then It's obvious that this is a user error (correct would be this == $elem). It results in the stack dump given below. But the question is: does the diagnostic have to be the way it is? The rule where the insert is doesn't help, and neither does the actual class of the object. Normally, I'd expect that a compiler detects such an error, as the Java compiler does. -W Caused by: org.drools.RuntimeDroolsException: Conversion to long not supported from rss.bfz.cfg.jaxb.elrep.MaSigType at org.drools.base.extractors.BaseObjectClassFieldReader.getLongValue(BaseObjectClassFieldReader.java:156) at org.drools.base.ClassFieldReader.getLongValue(ClassFieldReader.java:167) at org.drools.rule.VariableRestriction$LongVariableContextEntry.updateFromTuple(VariableRestriction.java:455) at org.drools.common.SingleBetaConstraints.updateFromTuple(SingleBetaConstraints.java:108) at org.drools.reteoo.JoinNode.assertLeftTuple(JoinNode.java:91) at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:197) at org.drools.reteoo.SingleLeftTupleSinkAdapter.createAndPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:146) at org.drools.reteoo.LeftInputAdapterNode.assertObject(LeftInputAdapterNode.java:158) at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:59) at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:215) at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:244) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:330) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:291) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:886) at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:180) at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:174) at rss.ixl.route.Rule_ERS__start_collecting_elements_on_regular_route.defaultConsequence(Rule_ERS__start_collecting_elements_on_regular_route.java:12) at rss.ixl.route.Rule_ERS__start_collecting_elements_on_regular_routeDefaultConsequenceInvoker.evaluate(Unknown Source) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1091)