Cann't debug in eclipse

Hi. I am new to the Drools. I used the Drools eclipse plug-in function.

I tried to toggled a break-point in the .drl (the rule file) and tried to run the program as a Drools project.

However, I got an error message as following:
java.lang.RuntimeException: no debugger registered to handle breakpoint
at org.mvel2.debug.DebuggerContext.checkBreak(DebuggerContext.java:98)
at org.mvel2.MVELRuntime.execute(MVELRuntime.java:76)
at org.mvel2.compiler.CompiledExpression.getDirectValue(CompiledExpression.java:123)
at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:119)
at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:113)
at org.mvel2.MVEL.executeExpression(MVEL.java:930)
at org.drools.core.util.MVELSafeHelper$RawMVELEvaluator.executeExpression(MVELSafeHelper.java:496)
at org.drools.core.rule.constraint.MvelConditionEvaluator.evaluate(MvelConditionEvaluator.java:92)
at org.drools.core.rule.constraint.MvelConditionEvaluator.evaluate(MvelConditionEvaluator.java:77)
at org.drools.core.rule.constraint.MvelConstraint.evaluate(MvelConstraint.java:248)
at org.drools.core.rule.constraint.MvelConstraint.isAllowed(MvelConstraint.java:204)
at org.drools.core.reteoo.AlphaNode.assertObject(AlphaNode.java:141)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:494)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:374)
at org.drools.core.reteoo.ObjectTypeNode.propagateAssert(ObjectTypeNode.java:298)
at org.drools.core.phreak.PropagationEntry$Insert.execute(PropagationEntry.java:93)
at org.drools.core.phreak.SynchronizedPropagationList.flush(SynchronizedPropagationList.java:96)
at org.drools.core.phreak.SynchronizedPropagationList.flush(SynchronizedPropagationList.java:69)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.flushPropagations(StatefulKnowledgeSessionImpl.java:1993)
at org.drools.core.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1289)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.internalFireAllRules(StatefulKnowledgeSessionImpl.java:1294)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:1281)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:1260)
at com.sample.DroolsTest.main(DroolsTest.java:24)

How could I fix this problem?

Thanks!