404 error when referencing fileUpload interceptor in Struts 2

I am using struts.xml file which is described below :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
   "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
   "http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
   <constant name="struts.devMode" value="true" />
   <constant name="struts.multipart.maxSize" value="1000000" />
   
   <package name="helloworld" extends="struts-default">
      
      <interceptors>
         <interceptor name="myinterceptor"
            class="com.struts2examples.MyInterceptor" />
         <interceptor name="myinterceptor1"
            class="com.struts2examples.MyInterceptor1" />
         
      </interceptors>
      
      <action name="hello" 
            class="com.struts2examples.HelloWorldAction" 
            method="execute">
            <result name="success">/HelloWorld.jsp</result>
            <result name="error">/AccessDenied.jsp</result>
            <interceptor-ref name="params"/>
            <interceptor-ref name="myinterceptor"/>
            <interceptor-ref name="myinterceptor1"/>
      </action>
      
      <action name="hello1" 
            class="com.struts2examples.HelloWorldAction1" 
            method="execute">
            <result name="success" type="freemarker">
                <param name="location">/hello.fm</param>
            </result>
            <result name="nopassnofail" type="redirect">
                <param name="location">/NewWorld.jsp</param >
            </result>
            <result name="error">/AccessDenied.jsp</result>
      </action>
      
      <action name="upload" class="com.struts2examples.UploadFile" method="execute">
      
       <interceptor-ref name="fileUpload">
           <param name="allowedTypes">image/jpeg,image/gif</param>
       </interceptor-ref>
       <result name="success">/success.jsp</result>
       <result name="error">/error.jsp</result>
      </action>
   </package>
</struts>

It was working before I added the last action upload. When I start the server it is showing me the 404 error. Can somebody help me out in resolving the issue. I am feeling that the issue is due to <interceptor-ref name="fileUpload">.

Answer

Try to add after <interceptor-ref name="fileUpload"> <interceptor-ref name="defaultStack">. If you add explicit interceptor to the action the defaultStack disappears.