NoClassDefFoundError: Signup

2012-05-09 16:18:30,820 ERROR [main] [confluence.plugin.descriptor.XWorkModuleDescriptor] getPackages Could not add package: {PackageConfig Name:i
nvite-public namespace:/invite abstract:false parents:[{PackageConfig Name:default namespace: abstract:false parents:[]}]} because: com.opensympho
ny.xwork.config.ConfigurationException: Unable to load Action class [com.atlassian.confluence.extra.invite.InviteSignupAction], skipping action [s
ignup]
    with nested exception 
java.lang.NoClassDefFoundError: com/atlassian/confluence/user/actions/SignupAction
com.opensymphony.xwork.config.ConfigurationException: Unable to load Action class [com.atlassian.confluence.extra.invite.InviteSignupAction], skip
ping action [signup]
    with nested exception 
java.lang.NoClassDefFoundError: com/atlassian/confluence/user/actions/SignupAction
        at com.atlassian.confluence.plugin.descriptor.XWorkModuleDescriptor.addAction(XWorkModuleDescriptor.java:305)
        at com.atlassian.confluence.plugin.descriptor.XWorkModuleDescriptor.getPackages(XWorkModuleDescriptor.java:132)
        at com.atlassian.confluence.plugin.descriptor.XWorkModuleDescriptor.getPackages(XWorkModuleDescriptor.java:526)
        at com.atlassian.confluence.plugin.descriptor.XWorkModuleDescriptor.init(XWorkModuleDescriptor.java:499)
        at com.opensymphony.xwork.config.impl.DefaultConfiguration.reload(DefaultConfiguration.java:85)
        at com.atlassian.confluence.event.listeners.XWorkChangeListener.handleXWorkStateChangeEvent(XWorkChangeListener.java:15)
        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 com.atlassian.event.internal.SingleParameterMethodListenerInvoker.invoke(SingleParameterMethodListenerInvoker.java:36)
        at com.atlassian.event.internal.AsynchronousAbleEventDispatcher$2.run(AsynchronousAbleEventDispatcher.java:60)
        at com.atlassian.event.internal.AsynchronousAbleEventDispatcher$1.execute(AsynchronousAbleEventDispatcher.java:28)
        at com.atlassian.event.internal.AsynchronousAbleEventDispatcher.dispatch(AsynchronousAbleEventDispatcher.java:56)
        at com.atlassian.event.internal.EventPublisherImpl.invokeListeners(EventPublisherImpl.java:151)
        at com.atlassian.event.internal.EventPublisherImpl.publish(EventPublisherImpl.java:70)
        at com.atlassian.confluence.plugin.ConfluencePluginManager.init(ConfluencePluginManager.java:203)
        at com.atlassian.confluence.plugin.PluginFrameworkContextListener.contextInitialized(PluginFrameworkContextListener.java:52)
        at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4206)
        at org.apache.catalina.core.StandardContext.start(StandardContext.java:4705)
        at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1057)
        at org.apache.catalina.core.StandardHost.start(StandardHost.java:840)
        at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1057)
        at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:463)
        at org.apache.catalina.core.StandardService.start(StandardService.java:525)
        at org.apache.catalina.core.StandardServer.start(StandardServer.java:754)
        at org.apache.catalina.startup.Catalina.start(Catalina.java:595)
        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:289)
        at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)
with nested exception java.lang.NoClassDefFoundError: com/atlassian/confluence/user/actions/SignupAction