javax.servlet.ServletException: java.lang.NoClassDefFoundError: javax/el/ELResolver错误解决办法...

错误如下，不知道是不是遇到鬼了，之前好好的，装了myeclipse以后出错了（说实话，myeclipse用的很不爽，感觉netbeans更好用些）

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: java.lang.NoClassDefFoundError: javax/el/ELResolver
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:268)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause

java.lang.NoClassDefFoundError: javax/el/ELResolver
    java.lang.ClassLoader.defineClass1(Native Method)
    java.lang.ClassLoader.defineClass(ClassLoader.java:620)
    java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
    java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
    java.net.URLClassLoader.access$000(URLClassLoader.java:56)
    java.net.URLClassLoader$1.run(URLClassLoader.java:195)
    java.security.AccessController.doPrivileged(Native Method)
    java.net.URLClassLoader.findClass(URLClassLoader.java:188)
    java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    java.lang.ClassLoader.loadClass(ClassLoader.java:299)
    sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
    java.lang.ClassLoader.loadClass(ClassLoader.java:299)
    java.lang.ClassLoader.loadClass(ClassLoader.java:251)
    java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
    org.apache.jasper.runtime.JspFactoryImpl.getJspApplicationContext(JspFactoryImpl.java:209)
    org.apache.jsp.index_jsp._jspInit(index_jsp.java:22)
    org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)
    org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:164)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:340)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.35 logs.