NoSuchMethodError: org.apache.commons.collections.IteratorUtils.emptyIterator()

这是什么原因啊，有人会吗？在网上找了好久也没有解决。
2011-8-13 11:06:43 org.apache.catalina.core.StandardContext listenerStart
严重: Exception sending context initialized event to listener instance of class com.liferay.portal.spring.context.PortalContextLoaderListener
java.lang.NoSuchMethodError: org.apache.commons.collections.IteratorUtils.emptyIterator()Lorg/apache/commons/collections/ResettableIterator;
at org.apache.commons.configuration.PropertyConverter.toIterator(PropertyConverter.java:882)
at org.apache.commons.configuration.AbstractConfiguration.addPropertyValues(AbstractConfiguration.java:416)
at org.apache.commons.configuration.AbstractConfiguration.addProperty(AbstractConfiguration.java:389)
at com.germinus.easyconf.AggregatedProperties.addIncludedPropertiesSources(AggregatedProperties.java:215)
at com.germinus.easyconf.AggregatedProperties.addFileProperties(AggregatedProperties.java:180)
at com.germinus.easyconf.AggregatedProperties.addPropertiesSource(AggregatedProperties.java:140)
at com.germinus.easyconf.AggregatedProperties.addBaseFileName(AggregatedProperties.java:116)
at com.germinus.easyconf.ConfigurationLoader.readPropertiesConfiguration(ConfigurationLoader.java:54)
at com.germinus.easyconf.ComponentConfiguration.getAvailableProperties(ComponentConfiguration.java:152)
at com.germinus.easyconf.ComponentConfiguration.getProperties(ComponentConfiguration.java:140)
at com.liferay.portal.configuration.ConfigurationImpl.getComponentProperties(ConfigurationImpl.java:338)
at com.liferay.portal.configuration.ConfigurationImpl.printSources(ConfigurationImpl.java:390)
at com.liferay.portal.configuration.ConfigurationImpl.<init>(ConfigurationImpl.java:133)
at com.liferay.portal.configuration.ConfigurationImpl.<init>(ConfigurationImpl.java:72)
at com.liferay.portal.util.PropsUtil.<init>(PropsUtil.java:93)
at com.liferay.portal.util.PropsUtil.<clinit>(PropsUtil.java:225)
at com.liferay.portal.spring.context.PortalApplicationContext.loadBeanDefinitions(PortalApplicationContext.java:63)
at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:92)
at org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory(AbstractRefreshableApplicationContext.java:123)
at org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:422)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:352)
at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:255)
at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:199)
at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:45)
at com.liferay.portal.spring.context.PortalContextLoaderListener.contextInitialized(PortalContextLoaderListener.java:49)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3795)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4252)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:760)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:740)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:544)
at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:626)
at org.apache.catalina.startup.HostConfig.deployDescriptors(HostConfig.java:553)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:488)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1150)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:311)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:120)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1022)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:736)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
at org.apache.catalina.core.StandardService.start(StandardService.java:448)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:700)
at org.apache.catalina.startup.Catalina.start(Catalina.java:552)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:295)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:433)