500 Internal Server Error <PRE> <B>/webtest/jrun/test.jsp:</B> Exception thrown processing JSP page. java.lang.NoClassDefFoundError at org.apache.struts.taglib.html.FormTag.lookup(FormTag.java:795) at org.apache.struts.taglib.html.FormTag.doStartTag(FormTag.java:506) at jrun__jrun__test2ejspe._jspService(jrun__jrun__test2ejspe.java:50) at allaire.jrun.jsp.HttpJSPServlet.service(HttpJSPServlet.java:39) at allaire.jrun.jsp.JSPServlet.service(JSPServlet.java:228) at allaire.jrun.jsp.JSPServlet.service(JSPServlet.java:196) at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1417) at allaire.jrun.session.JRunSessionService.service(JRunSessionService.java:1106) at allaire.jrun.servlet.JRunSE.runServlet(JRunSE.java:1271) at allaire.jrun.servlet.JRunRequestDispatcher.forward(JRunRequestDispatcher.java:89) at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1557) at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1547) at allaire.jrun.servlet.JvmContext.dispatch(JvmContext.java:364) at allaire.jrun.http.WebEndpoint.run(WebEndpoint.java:115) at allaire.jrun.ThreadPool.run(ThreadPool.java:272) at allaire.jrun.WorkerThread.run(WorkerThread.java:75) </PRE> 这是什么原因?
<PRE> <B>/webtest/jrun/test.jsp:</B> Exception thrown processing JSP page. java.lang.NoClassDefFoundError at org.apache.struts.taglib.html.FormTag.lookup(FormTag.java:795) at org.apache.struts.taglib.html.FormTag.doStartTag(FormTag.java:506) at jrun__jrun__test2ejspe._jspService(jrun__jrun__test2ejspe.java:50) at allaire.jrun.jsp.HttpJSPServlet.service(HttpJSPServlet.java:39) at allaire.jrun.jsp.JSPServlet.service(JSPServlet.java:228) at allaire.jrun.jsp.JSPServlet.service(JSPServlet.java:196) at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1417) at allaire.jrun.session.JRunSessionService.service(JRunSessionService.java:1106) at allaire.jrun.servlet.JRunSE.runServlet(JRunSE.java:1271) at allaire.jrun.servlet.JRunRequestDispatcher.forward(JRunRequestDispatcher.java:89) at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1557) at allaire.jrun.servlet.JRunSE.service(JRunSE.java:1547) at allaire.jrun.servlet.JvmContext.dispatch(JvmContext.java:364) at allaire.jrun.http.WebEndpoint.run(WebEndpoint.java:115) at allaire.jrun.ThreadPool.run(ThreadPool.java:272) at allaire.jrun.WorkerThread.run(WorkerThread.java:75) </PRE>
这是什么原因?