请问这是什么错误...Bean应该没错

显示错误信息是这样:
type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: Expression: '#{usermanagBean.uname}'
javax.faces.webapp.FacesServlet.service(FacesServlet.java:125)
root cause javax.faces.FacesException: Expression: '#{usermanagBean.uname}'
org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:411)
org.apache.myfaces.application.jsp.JspViewHandlerImpl.renderView(JspViewHandlerImpl.java:280)
org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:300)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:110)
----------------------------------------------------------
UserManagBean是这样的
package com.eos.web.vo;import com.eos.data.hibernate.FacesUtils;import com.eos.model.exception.EosException;
import com.eos.web.bo.UserManag;
public class UserManagBean extends UserManagBaseBean {

private String uname; private String upassword;
private UserManag usermanag=new UserManag();

public String getUpassword() {
return upassword;
} public void setUpassword(String upassword) {
this.upassword = upassword;
}
public String getUname() {
return uname;
} public void setUname(String uname) {
this.uname = uname;
} public UserManag getUsermanag() {
return usermanag;
}
public void setUser(UserManag usermanag) {
this.usermanag = usermanag;
}//  登录事件
public String loginAction() throws EosException{
UserManag usermanag=this.getUsermanagService().login(uname,upassword);
if (usermanag == null) {
FacesUtils.addErrorMessage("用户名错误或密码错误！");
return "";
}
return "Login:success"; }
// 退出事件
public String logoutAction(){
return null;
}
//  回首页
public String back() {
String back;
if (usermanag.getFlag()) {
back = "back_to_admin";
} else {
back = "back_to_teacher";
}
return back;
}}---------------------------------------------------------------jsp页面是这样的:
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h"%>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f"%>
<%@ page pageEncoding="gb2312"%> 
<%@ page contentType="text/html; charset=gb2312"%>
<html> <head>
<title>企业办公管理系统 V1.0</title>
<LINK href="/twms/public/css/public.css" type=text/css rel=stylesheet>
</head> <body>
<f:view>
<table width="100%" height="95%" border="0" cellpadding="0" cellspacing="0">
<tr>
</tr>
<tr>
<td background="/EOS/images/login_02.gif" height="30%"></td>
</tr> <tr>
<td width="100%" height="389" background="/EOS/images/login_04.jpg">
<table width="100%" height="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td width="140" height="389">
&nbsp;
</td>
<td width="442">
<table width="100%" height="389" border="0" cellspacing="0" cellpadding="0">
<tr>
<td height=80>
&nbsp;
</td>
</tr>
<tr>
<td valign=top>
<h:form>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td align="left"  colspan="2"> <h:messages globalOnly="true" style="text-align:left;color:#ff0000;"/>
</td>
<td></td>
</tr>
<tr>
<td align="center">
用户名 </td>
<td height="25" align="left"> <h:inputText value="#{usermanagBean.uname}" required="true" styleClass="editor" size="13" id="用户名"></h:inputText> </td> <TD width="50%" valign="middle">
<h:message for="用户名" style="color:#ff0000;"/>
</TD>
</tr>
<tr>
<td align="center">
密&nbsp;&nbsp;码 </td>
<td align="left" height="25"> <h:inputSecret size="15" styleClass="editor" required="true" value="#{usermanagBean.upassword}" id="密码"></h:inputSecret> </td>
<TD width="50%" valign="middle">
<h:message for="密码" style="color:#ff0000;"/>
</TD>
</tr>
<tr>
<td height=10></td>
</tr>
<tr>

<td align=right  colspan="2">
<h:commandButton type="submit" value="登录" action="#{usermanagBean.loginAction}"></h:commandButton>
&nbsp;&nbsp;&nbsp;&nbsp;
<h:commandButton type="reset" value="重置" immediate="true"></h:commandButton>
</td>
<td align=center> </td>
</tr>
</table>
</h:form>
</td>
</tr>
<tr>
<td>
&nbsp;
</td>
</tr>
</table>
</td>
<td valign=top>
<table width="30%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td width="19%" height="105">
&nbsp;
</td>
<td width="81%">
&nbsp;
</td>
</tr>
<tr>
<td height="40" colspan=2> </td>
</tr>
</table>
</td>
</tr>
</table>
</td>
</tr> </table>
<tr>
<%@ include file="footer.jsp"%>
</tr>
</f:view> </body>
</html>但是一运行tomcat就出现最上面的错,不能显示页面...是什么原因,求教