jivejdon3中统计在线人数监听器加载报异常

分解jivejdon3部署在tomcat6.0，启动项目是报如下异常：
严重: Null component Catalina:type=JspMonitor,name=jsp,WebModule=//localhost/jivejdon3,J2EEApplication=none,J2EEServer=none
2009-12-21 16:57:15 org.apache.catalina.startup.HostConfig deployDirectory
严重: Error deploying web application directory jivejdon3
java.lang.UnsupportedClassVersionError: Bad version number in .class file (unable to load class com.jdon.jivejdon.presentation.listener.UserCounterListener)

哪位能指点下是什么原因，谢谢！