java.lang.NoSuchFieldError: DESCR

When I try the http://www.softwarepassion.com/getting-started-with-drools-flow/ tutorial I get this exception:

Exception in thread "main" java.lang.NoSuchFieldError: DESCR
       at
org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:539)
       at
org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilder开发者_Python百科Impl.java:28)
       at
com.softwarepassion.droolsflow.SPDroolsFlowExample.readKnowledgeBase(SPDroolsFlowExample.java:30)
       at
com.softwarepassion.droolsflow.SPDroolsFlowExample.main(SPDroolsFlowExample.java:20)

How can I resolve this?

This usually indicates incompatible versions of two libraries. Get the most up-to-date jars of drools and try again. Also make sure you don't have multiple versions on the classpath.