Can anyone explain what this ConsequenceException means? 

Exception in thread "main" org.drools.runtime.rule.ConsequenceException: java.lang.ClassCastException: org.drools.reteoo.AlphaNode$AlphaMemory cannot be cast to org.drools.reteoo.BetaMemory

      at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:23)

      at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:943)

      at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:885)

      at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1086)

      at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:660)

      at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:627)

      at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:183)

      at org.jcvi.annotation.rulesengine.RulesEngine.fireAllRules(RulesEngine.java:210)

      at org.jcvi.annotation.Aruba.run(Aruba.java:311)

      at org.jcvi.annotation.RunTest.main(RunTest.java:55)

Nelson