Ajax not working on IE. Undefined error

Hi guys this is my first post here.
I am working with struts 2.1.6 and struts-dojo-plugin 2.1.6.
I´m trying to do a simple operation, just updating the content of a div with AJAX.
The operation works with Firefox and Chrome but it fails on IE throwing an undefined error on the target div.

I am posting my main jsp, the content jsp, the action class, struts.xml, and web.xml.
I am also attaching a screenshot with the undefined error on IE.

Here it´s my JSP:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/2000/REC-xhtml1-20000126/DTD/xhtml1-transitional.dtd">

<%@page import="com.desafiodt.model.Jugador"%><html xmlns="http://www.w3.org/1999/xhtml">
<head>
	<meta http-equiv="content-type" content="text/html; charset=iso-8859-1" />
		<link rel="stylesheet" type="text/css" href="estilo1.css" />
		<link rel="stylesheet" type="text/css" href="css/cssverticalmenu.css" />
		<%@ taglib uri="/struts-tags" prefix="s"%>
		<%@ taglib uri="http://displaytag.sf.net" prefix="display" %>
		<%@ taglib uri="/struts-dojo-tags" prefix="sx" %>

/***********************************************

* CSS Vertical List Menu- by JavaScript Kit (www.javascriptkit.com)
* Menu interface credits: http://www.dynamicdrive.com/style/csslibrary/item/glossy-vertical-menu/ 
* This notice must stay intact for usage
* Visit JavaScript Kit at http://www.javascriptkit.com/ for this script and 100s more

***********************************************/

</script>

<title>Desafío DT</title> 
</head> 
 
 <sx:head parseContent="true" debug="false" />
<body>
<s:form action="Plantel_aceptar">
<s:hidden id="hiddenTitulares" name="hiddenTitulares"></s:hidden>
<s:include value="menu.jsp"></s:include>
<br></br><br></br><br></br>
<table>
	<tr>
		<td valign="top" class="columnaIzquierda" >
		<br></br>
		<br></br>
				<ul id="verticalmenu" class="glossymenu">
				 
						<li><a href="#">Plantel</a>
						<ul>
							<li><s:url id="emitirRecibo" action="EmitirReciboMensual_input">
							</s:url><s:a href="%{emitirRecibo}" 
							onclick="window.open(this.href,'window','width=880, height=630,top=40,left=50 scrollbars=yes, status=yes, resizable=yes');return false">
							Alineacion</s:a></li>
							
							<li><s:url id="cancelarRecibo" action="EmitirReciboMensual_cancelarRecibo">
							</s:url><s:a href="%{cancelarRecibo}" 
							onclick="window.open(this.href,'window','width=880, height=630,top=40,left=50 scrollbars=yes, status=yes, resizable=yes');return false">
							Transferencias</s:a></li>	
						</ul>
						</li>				 
						<li><a href="#">Ligas</a>
						<ul>
							<li>
							<s:url id="ajaxCallUrl"  action="Ligas_handleAjaxInput">
            				</s:url>
        					<sx:a href="%{ajaxCallUrl}" targets="content" notifyTopics="content" >
							Crear liga gratuita</sx:a>										
							</li>
							
							<li><s:url id="ligaApuestas" action="Ligas_crearLigaApuestas">
							</s:url><s:a href="%{ligaApuestas}">
							Crear liga apuestas</s:a></li>
							
							<li><s:url id="verContrato" action="Contrata_input">
							</s:url><s:a href="%{verContrato}"
							onclick="window.open(this.href,'window','width=690, height=400,top=150,left=150 scrollbars=yes, status=yes');return false">
							Registrarse a liga</s:a></li>
							 							
							<li><s:url id="verFamiliares" action="Familiar_input">
							</s:url><s:a href="%{verFamiliares}"
							onclick="window.open(this.href,'window','width=650, height=460,top=150,left=150 scrollbars=yes, status=yes');return false">
							Invitar amigos</s:a></li>
						</ul>
						</li>
				</ul>

</td>
		<td class="padding2" >
			  <sx:div id="content" >
        	  </sx:div>
			 
		</td>
	</tr>

</table>
</s:form>	
</body>
</html>

Here it´s my content JSP:

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=iso-8859-1" />
<link rel="stylesheet" type="text/css" href="estilo1.css" />
<link rel="stylesheet" type="text/css" href="css/cssverticalmenu.css" />
<%@ taglib uri="/struts-tags" prefix="s"%>
<%@ taglib uri="/struts-dojo-tags" prefix="sx"%>

<title>Desafío DT</title>
 
<sx:head/>
</head>

<body>
<s:form action="Ligas" > 
 
<table>
	<tr>
	<td valign="top" class="columnaIzquierda" >
	</td>
	<td class="padding2" align="center" >
	<div class="roundedcornr_box">
			  <div class="roundedcornr_top"><div></div></div>
			    <div class="roundedcornr_content">
		 <div class="formulario">
		 <h1 class="titulo">Crear liga</h1>
		<table>
			<tr>
			<td>
			
			  <table>
			  		<tr>
						<td align="left">Nombre:</td>
						<td>
						<s:textfield key="nombre" name="nombre" ></s:textfield>
						</td>
					</tr>
					<tr>
						<td align="left">Código:</td>
						<td>
						<s:textfield key="codigo"  name="codigo"></s:textfield>
						(Este código será enviado a tus amigos para que puedan registrarse a la liga)
						</td>
					</tr>
					<tr>
						<td colspan="2">							
						<s:submit value="Siguiente" action="Ligas_registrarAmigos"></s:submit>
						</td>
					</tr>
					
				</table>
							 
			</td>
			</tr>
			<tr>
				<td colspan="2" align="left">	
					<s:actionerror/>				
					<s:actionmessage/>
				</td>
			</tr>
					
			</table>
			</div>
		</div>
		<div class="roundedcornr_bottom"><div></div></div>
		</div>		
			
	</td>
	</tr>

</table>
</s:form>

</body>
</html>

Here it´s my action:

Here it´s my struts.xml:

Finally, here it´s my web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" 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 http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 
  <display-name>DesafioDT</display-name>
		
	<context-param>
		<param-name>webAppRootKey</param-name>
		<param-value>DesafioDT.root</param-value>
	</context-param>
 
 	   	
	
    	
	 
			  
	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>classpath:conf/LOCAL/applicationContext.xml</param-value>
	</context-param> 	
	
	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>
    
    <filter>
        <filter-name>struts2</filter-name>
        <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
    </filter>

<filter-mapping>
        <filter-name>struts2</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

<welcome-file-list>
        <welcome-file>/home.jsp</welcome-file>
    </welcome-file-list>
    	 		
   
		 
</web-app>

Any help will be great appretiated.
Many thanks in advance,
Regards.