当我尝试 http://www.softwarepassion.com/getting-started-with-drools-flow/教程时，我得到了这个异常：
Exception in thread "main" java.lang.NoSuchFieldError: DESCR
at
org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:539)
at
org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:28)
at
com.softwarepassion.droolsflow.SPDroolsFlowExample.readKnowledgeBase(SPDroolsFlowExample.java:30)
at
com.softwarepassion.droolsflow.SPDroolsFlowExample.main(SPDroolsFlowExample.java:20)
我该如何解决这个问题？