IncompatibleClassChangeError using feedburner plugin on 2.6

2007-09-09 19:39:15,104 ERROR [resin-tcp-connection-j2ee.confluence.atlassian.com:8080-801] [opensymphony.webwork.dispatcher.ServletDispatcher] serviceAction Could not execute action
 -- url: /plugins/feedburner/popularitemsfeed.action | userName: anonymous
com.atlassian.core.exception.InfrastructureException: java.lang.IncompatibleClassChangeError
	at com.atlassian.xwork.interceptors.XWorkTransactionInterceptor.intercept(XWorkTransactionInterceptor.java:116)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.opensymphony.xwork.DefaultActionProxy.execute(DefaultActionProxy.java:115)
	at com.opensymphony.webwork.dispatcher.ServletDispatcher.serviceAction(ServletDispatcher.java:229)
	at com.opensymphony.webwork.dispatcher.ServletDispatcher.service(ServletDispatcher.java:199)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:92)
	at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:106)
	at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:118)
	at com.atlassian.confluence.util.profiling.ProfilingPageFilter.parsePage(ProfilingPageFilter.java:137)
	at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:54)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.core.filters.ServletContextThreadLocalFilter.doFilter(ServletContextThreadLocalFilter.java:21)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.confluence.util.LoggingContextFilter.doFilter(LoggingContextFilter.java:46)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.confluence.util.UserThreadLocalFilter.doFilter(UserThreadLocalFilter.java:44)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.seraph.filter.SecurityFilter.doFilter(SecurityFilter.java:182)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.seraph.filter.LoginFilter.doFilter(LoginFilter.java:159)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.confluence.util.ClusterHeaderFilter.doFilter(ClusterHeaderFilter.java:35)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.johnson.filters.JohnsonFilter.doFilter(JohnsonFilter.java:96)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at org.springframework.orm.hibernate.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:174)
	at com.atlassian.spring.filter.FlushingSpringSessionInViewFilter.doFilterInternal(FlushingSpringSessionInViewFilter.java:29)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.util.profiling.filters.ProfilingFilter.doFilter(ProfilingFilter.java:140)
	at com.atlassian.core.filters.ProfilingAndErrorFilter.doFilter(ProfilingAndErrorFilter.java:27)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.confluence.util.RequestCacheThreadLocalFilter.doFilter(RequestCacheThreadLocalFilter.java:25)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.core.filters.gzip.GzipFilter.doFilter(GzipFilter.java:57)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.core.filters.AbstractEncodingFilter.doFilter(AbstractEncodingFilter.java:37)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:173)
	at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:229)
	at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:274)
	at com.caucho.server.port.TcpConnection.run(TcpConnection.java:511)
	at com.caucho.util.ThreadPool.runTasks(ThreadPool.java:520)
	at com.caucho.util.ThreadPool.run(ThreadPool.java:442)
	at java.lang.Thread.run(Thread.java:595)
Caused by: java.lang.IncompatibleClassChangeError
	at com.atlassian.confluence.plugin.feedburner.retrieval.ItemDataUrlBuilder.buildUrl(ItemDataUrlBuilder.java:10)
	at com.atlassian.confluence.plugin.feedburner.DefaultItemDataManager.getItemData(DefaultItemDataManager.java:20)
	at com.atlassian.confluence.plugin.feedburner.PopularItemsFeedAction.execute(PopularItemsFeedAction.java:31)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:168)
	at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.atlassian.confluence.util.LoggingContextInterceptor.intercept(LoggingContextInterceptor.java:48)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.atlassian.confluence.security.actions.PermissionCheckInterceptor.intercept(PermissionCheckInterceptor.java:47)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.atlassian.confluence.pages.actions.PageAwareInterceptor.intercept(PageAwareInterceptor.java:114)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.atlassian.confluence.spaces.actions.SpaceAwareInterceptor.intercept(SpaceAwareInterceptor.java:67)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.atlassian.confluence.core.actions.LastModifiedInterceptor.intercept(LastModifiedInterceptor.java:39)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.atlassian.confluence.core.ConfluenceAutowireInterceptor.intercept(ConfluenceAutowireInterceptor.java:25)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.atlassian.xwork.interceptors.XWorkTransactionInterceptor.intercept(XWorkTransactionInterceptor.java:98)
	... 46 more