高手请赐教，出现java.lang.NoClassDefFoundError: javax/servlet/jsp/PageContext的错误

我在用SmartUpload类上传文件时，
SmartUpload mySmartUpload = new SmartUpload();
mySmartUpload.initialize(pageContext);总报Error 500: javax/servlet/jsp/PageContext的错误，或者其它地方使用到
javax/servlet/jsp/PageContext类时都会报此类错误，请问这是为什么！？错误如下
[07-10-29 14:56:16:969 CST] 772e3da1 WebGroup      E SRVE0026E: ［Servlet 错误］－［javax/servlet/jsp/PageContext］：java.lang.NoClassDefFoundError: javax/servlet/jsp/PageContext
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:1753)
at java.lang.Class.getDeclaredMethods(Class.java:1219)
at java.beans.Introspector$1.run(Introspector.java:1120)
at java.security.AccessController.doPrivileged(Native Method)
at java.beans.Introspector.getPublicDeclaredMethods(Introspector.java:1118)
at java.beans.Introspector.getTargetMethodInfo(Introspector.java:983)
at java.beans.Introspector.getBeanInfo(Introspector.java(Inlined Compiled Code))
at java.beans.Introspector.getBeanInfo(Introspector.java(Compiled Code))
at org.apache.jasper.runtime.JspRuntimeLibrary.getWriteMethod(JspRuntimeLibrary.java:789)
at org.apache.jasper.runtime.JspRuntimeLibrary$2.run(JspRuntimeLibrary.java:551)
at com.ibm.ws.security.util.AccessController.doPrivileged(AccessController.java(Compiled Code))
at org.apache.jasper.runtime.JspRuntimeLibrary.handleSetProperty(JspRuntimeLibrary.java:548)
at org.apache.jsp._errorpage._jspService(_errorpage.java:133)
at com.ibm.ws.webcontainer.jsp.runtime.HttpJspBase.service(HttpJspBase.java(Compiled Code))
at javax.servlet.http.HttpServlet.service(HttpServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.jsp.servlet.JspServlet$JspServletWrapper.service(JspServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.jsp.servlet.JspServlet.serviceJspFile(JspServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.jsp.servlet.JspServlet.service(JspServlet.java(Compiled Code))
at javax.servlet.http.HttpServlet.service(HttpServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.StrictServletInstance.doService(StrictServletInstance.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.StrictLifecycleServlet._service(StrictLifecycleServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.ServicingServletState.service(StrictLifecycleServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.StrictLifecycleServlet.service(StrictLifecycleServlet.java(Inlined Compiled Code))
at com.ibm.ws.webcontainer.servlet.ServletInstance.service(ServletInstance.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.ValidServletReferenceState.dispatch(ValidServletReferenceState.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.ServletInstanceReference.dispatch(ServletInstanceReference.java(Inlined Compiled Code))
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.handleWebAppDispatch(WebAppRequestDispatcher.java(Compiled Code))
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.dispatch(WebAppRequestDispatcher.java(Compiled Code))
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java(Compiled Code))
at org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:498)
at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:542)
at org.apache.jsp._sal_5F_impexl_5F_result._jspService(_sal_5F_impexl_5F_result.java:344)
at com.ibm.ws.webcontainer.jsp.runtime.HttpJspBase.service(HttpJspBase.java(Compiled Code))
at javax.servlet.http.HttpServlet.service(HttpServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.jsp.servlet.JspServlet$JspServletWrapper.service(JspServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.jsp.servlet.JspServlet.serviceJspFile(JspServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.jsp.servlet.JspServlet.service(JspServlet.java(Compiled Code))
at javax.servlet.http.HttpServlet.service(HttpServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.StrictServletInstance.doService(StrictServletInstance.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.StrictLifecycleServlet._service(StrictLifecycleServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.IdleServletState.service(StrictLifecycleServlet.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.StrictLifecycleServlet.service(StrictLifecycleServlet.java(Inlined Compiled Code))
at com.ibm.ws.webcontainer.servlet.ServletInstance.service(ServletInstance.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.ValidServletReferenceState.dispatch(ValidServletReferenceState.java(Compiled Code))
at com.ibm.ws.webcontainer.servlet.ServletInstanceReference.dispatch(ServletInstanceReference.java(Inlined Compiled Code))
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.handleWebAppDispatch(WebAppRequestDispatcher.java(Compiled Code))
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.dispatch(WebAppRequestDispatcher.java(Compiled Code))
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java(Compiled Code))
at com.ibm.ws.webcontainer.srt.WebAppInvoker.doForward(WebAppInvoker.java(Compiled Code))
at com.ibm.ws.webcontainer.srt.WebAppInvoker.handleInvocationHook(WebAppInvoker.java(Compiled Code))
at com.ibm.ws.webcontainer.cache.invocation.CachedInvocation.handleInvocation(CachedInvocation.java(Compiled Code))
at com.ibm.ws.webcontainer.cache.invocation.CacheableInvocationContext.invoke(CacheableInvocationContext.java(Compiled Code))
at com.ibm.ws.webcontainer.srp.ServletRequestProcessor.dispatchByURI(ServletRequestProcessor.java(Compiled Code))
at com.ibm.ws.webcontainer.oselistener.OSEListenerDispatcher.service(OSEListener.java(Compiled Code))
at com.ibm.ws.webcontainer.http.HttpConnection.handleRequest(HttpConnection.java(Compiled Code))
at com.ibm.ws.http.HttpConnection.readAndHandleRequest(HttpConnection.java(Compiled Code))
at com.ibm.ws.http.HttpConnection.run(HttpConnection.java(Compiled Code))
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java(Compiled Code))