新手求解：使用JSF标签时出错

faces-config.xml、web.xml配置文件都配置了好几遍，也把JSF所使用的.jar包放在了WEB-INF/lib中，从网上下载的例子也是这样报错,纠结啊，这啥问题
Tomcat6.0运行时报错如下：
org.apache.jasper.JasperException: An exception occurred processing JSP page /index.jsp at line 118:     </head>
9:     <body>
10:     <h1>欢迎登录</h1>
11:     <f:view>
12:         <h:form>
13:             <p><h:outputText value="#{UserBean.errMessage}"/></p>
14:             <p>请输入名字：<h:inputText value="#{UserBean.name}"/></p>
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:519)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:428)
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)
root causejava.lang.RuntimeException: Cannot find FacesContext
javax.faces.webapp.UIComponentClassicTagBase.getFacesContext(UIComponentClassicTagBase.java:1855)
javax.faces.webapp.UIComponentClassicTagBase.setJspId(UIComponentClassicTagBase.java:1672)
org.apache.jsp.index_jsp._jspx_meth_f_005fview_005f0(index_jsp.java:109)
org.apache.jsp.index_jsp._jspService(index_jsp.java:83)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:386)
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)