HTTP Error 503 (SERVICE_UNAVAILABLE) using GWT

When I run the project I see in my browser a page with "HTTP ERROR: 503 / Problem accessing /WhereIsMatch.html. Reason: SERVICE_UNAVAILABLE"

This is my web.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
              http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5" xmlns="http://java.sun.com/xml/ns/javaee">

    <!-- Servlets -->
    <welcome-file-list>
        <welcome-file>WhereIsMatch.html</welcome-file>
    </welcome-file-list>

    <servlet>
        <servlet-name>matchServlet</servlet-name>
        <servlet-class>com.kernapps.whereismatch.server.rpc.MatchServiceImpl</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>matchServlet</servlet-name>
        <url-pattern>/whereismatch/match</url-pattern>
    </servlet-mapping>

    <!-- Default page to serve -->

</web-app>

And I put the corresponding java annotation on the class MatchService:

package com.kernapps.whereismatch.client.rpc;

import com.google.gwt.user.client.rpc.RemoteService;
import com.google.gwt.user.client.rpc.RemoteServiceRelativePath;
import com.kernapps.whereismatch.shared.domain.Match;
import com.kernapps.whereismatch.shared.domain.Matches;

@RemoteServiceRelativePath("match")
public interface MatchService extends RemoteService {
    public Match getMatch(int id);

    public Matches getMatchesCurrentRound();

}

Console puts:

Initializing App Engine server
19-jul-2013 19:29:10 com.google.apphosting.utils.config.AppEngineWebXmlReader readAppEngineWebXml
INFO: Successfully processed D:\Desarrollo\AISS\WhereIsMatch\war\WEB-INF/appengine-web.xml
19-jul-2013 19:29:10 com.google.apphosting.utils.config.AbstractConfigXmlReader readConfigXml
INFO: Successfully processed D:\Desarrollo\AISS\WhereIsMatch\war\WEB-INF/web.xml
19-jul-2013 19:29:10 com.google.appengine.tools.development.SystemPropertiesManager setSystemProperties
INFO: Overwriting system property key 'java.util.logging.config.file', value 'D:\Aplicaciones\eclipse Kepler\plugins\com.google.appengine.eclipse.sdkbundle_1.8.1.1\appengine-java-sdk-1.8.1.1\config\sdk\logging.properties' with value 'WEB-INF/logging.properties' from 'D:\Desarrollo\AISS\WhereIsMatch\war\WEB-INF\appengine-web.xml'
19-jul-2013 19:29:11 com.google.apphosting.utils.jetty.JettyLogger info
INFO: Logging to JettyLogger(null) via com.google.apphosting.utils.jetty.JettyLogger
19-jul-2013 19:29:13 com.google.apphosting.utils.jetty.JettyLogger info
INFO: jetty-6.1.x
19-jul-2013 19:29:35 com.google.apphosting.utils.jetty.JettyLogger info
INFO: Started SelectChannelConnector@0.0.0.0:8888
19-jul-2013 19:29:35 com.google.appengine.tools.development.AbstractServer startup
INFO: Server default is running at http://localhost:8888/
19-jul-2013 19:29:35 com.google.appengine.tools.development.AbstractServer startup
INFO: The admin console is running at http://localhost:8888/_ah/admin
19-jul-2013 19:29:35 com.google.appengine.tools.development.DevAppServerImpl start
INFO: Dev App Server is now running

How can I solve it?

I don't know why, but it was solved when I restarted Eclipse.