about tomcat-users.xml

Hi,

When i try to implement container managed security ,i got below exception. please can anyone explain me the problem?

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HTTP Status 400 - Invalid direct reference to form login page
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my web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee <a href="http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">" target="_blank" rel="nofollow">http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"></a>
   
   
   
   <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>
    
    
    <login-config>
        <auth-method>FORM</auth-method>
        <form-login-config>
            <form-login-page>/index.jsp</form-login-page>
            <form-error-page>/error.jsp</form-error-page>            
        </form-login-config>
    </login-config>
    
    <security-role>
        <role-name>author</role-name>        
    </security-role>
    
   <security-constraint>
       <web-resource-collection>
           <web-resource-name>sew</web-resource-name>
           <url-pattern>/success.jsp</url-pattern>
           <http-method>POST</http-method>
       </web-resource-collection>
     <auth-constraint>
        <role-name>author</role-name>        
     </auth-constraint>
   </security-constraint>   
   
    
        <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
        </welcome-file-list>
        
    </web-app>

my tomcat-users.xml