what does this mean?
2003-12-20 14:43:11 StandardContext[/balancer]Exception starting filter BalancerFilter java.lang.NoClassDefFoundError: org/apache/commons/digester/Digester at org.apache.webapp.balancer.RulesParser.createDigester(RulesParser.java:107) at org.apache.webapp.balancer.RulesParser.<init>(RulesParser.java:85) at org.apache.webapp.balancer.BalancerFilter.init(BalancerFilter.java:121) at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:272) at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:355) at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:126) at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:3646) at org.apache.catalina.core.StandardContext.start(StandardContext.java:4263) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:866) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:850) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:633) at org.apache.catalina.core.StandardHostDeployer.install(StandardHostDeployer.java:316) at org.apache.catalina.core.StandardHost.install(StandardHost.java:859) at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:723) at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:473) at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1002) at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:393) at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:166) at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1133) at org.apache.catalina.core.StandardHost.start(StandardHost.java:816) at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1125) at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:518) at org.apache.catalina.core.StandardService.start(StandardService.java:519) at org.apache.catalina.core.StandardServer.start(StandardServer.java:2343) at org.apache.catalina.startup.Catalina.start(Catalina.java:581) 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:324) at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:297) at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:398)
