[rules-users] Unable to resolve class x for identifier y

[Bojan Janisch]

Hey everyone,

I'm using Drools in a multithreaded environment where multiple KnowledgeBuilder and StatefulKnowledgeSessions are created parallel. Until now everything runs smooth, but suddenly I got this error:

Exception in thread "ECJ Evaluation Thread 5" org.drools.RuntimeDroolsException: Unable to resolve class 'de.fraunhofer.scai.bio.extraction.types.text.NormalizedNamedEntity' for identifier 'this
	at org.drools.base.mvel.MVELCompilationUnit.getCompiledExpression(MVELCompilationUnit.java:231)
	at org.drools.rule.constraint.MvelConstraint.createMvelConditionEvaluator(MvelConstraint.java:206)
	at org.drools.rule.constraint.MvelConstraint.evaluate(MvelConstraint.java:190)
	at org.drools.rule.constraint.MvelConstraint.isAllowedCachedLeft(MvelConstraint.java:169)
	at org.drools.common.SingleBetaConstraints.isAllowedCachedLeft(SingleBetaConstraints.java:125)
	at org.drools.reteoo.JoinNode.propagateFromLeft(JoinNode.java:105)
	at org.drools.reteoo.JoinNode.assertLeftTuple(JoinNode.java:95)
	at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:196)
	at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:71)
	at org.drools.reteoo.JoinNode.propagateFromRight(JoinNode.java:159)
	at org.drools.reteoo.JoinNode.assertObject(JoinNode.java:148)
	at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:59)
	at org.drools.reteoo.AlphaNode.assertObject(AlphaNode.java:141)
	at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:497)
	at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:382)
	at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:235)
	at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:240)
	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:350)
	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:311)
	at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:903)
	at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:847)
	at org.drools.impl.StatefulKnowledgeSessionImpl.insert(StatefulKnowledgeSessionImpl.java:269)
	at rulevolution.RulEvolution.runDrools(RulEvolution.java:310)
	at rulevolution.RulEvolution.evaluate(RulEvolution.java:161)
	at ec.simple.SimpleEvaluator.evalPopChunk(SimpleEvaluator.java:259)
	at ec.simple.SimpleEvaluator$SimpleEvaluatorThreadCG.run(SimpleEvaluator.java:341)
	at ec.util.ThreadPool$PoolThread.run(ThreadPool.java:57)

I don't know why it happened, my program already ran for about 15 minutes. Could someone explain me what could cause such an error? I didn't find much information about it in the internet. 

Thanks and greetings

Bojan