O elemento de configuração não está declarado

Eu estou fazendo algum trabalho no Visual Studio 2012 Express Edition. Eu adicionei um arquivo XML App.config da seguinte maneira:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
</configuration>

A primeira coisa que acontece é um aviso que diz "O elemento 'configuration' não está declarado". Alguém sabe por que isso está acontecendo? Parece que os elementos não podem ser declarados dentro até que isso seja resolvido.

Obrigado!

Este é todo o XML:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
<appSettings>
<add key="Version" value="779" />
<add key="TimeOut" value="60000" />
<add key="LogFileName" value="Log.txt" />
<!-- your Developer Id with eBay -->
<add key="Environment.DevId" value="" />
<!-- your Application Id with eBay -->
<add key="Environment.AppId" value="" />
<!-- your Application Certificate with eBay -->
<add key="Environment.CertId" value="" />
<!-- API Server URL -->
<!-- For production site use: https://api.ebay.com/wsapi -->
<!-- For Sandbox use: https://api.sandbox.ebay.com/wsapi -->
<add key="Environment.ApiServerUrl" value="https://api.sandbox.ebay.com/wsapi" />
<!-- EPS Server URL -->
<!-- For production site use: https://api.ebay.com/ws/api.dll"/-->
<add key="Environment.EpsServerUrl" value="https://api.sandbox.ebay.com/ws/api.dll" />
<!-- eBay Signin URL -->
<!-- For production site use: https://signin.ebay.com/ws/eBayISAPI.dll?SignIn -->
<!-- https://signin.sandbox.ebay.com/ws/eBayISAPI.dll?SignIn -->
<add key="Environment.SignInUrl" value="https://signin.sandbox.ebay.com/ws/eBayISAPI.dll?SignIn" />
<!-- ViewItem URL -->
<!-- For production site use: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&amp;item={0} -->
<add key="Environment.ViewItemUrl" value="http://cgi.sandbox.ebay.com/ws/eBayISAPI.dll?ViewItem&amp;item={0}" />
<!-- token is for both API server and EPS server -->
<add key="UserAccount.ApiToken" value="" />
<!-- eBay site ID -->
<add key="UserAccount.eBayUserSiteId" value="0" />
<add key="logexception" value="true"/>
<add key="logmessages" value="true"/>
<add key="logsdkmessages" value="true"/>
<add key="logsdk" value="true"/>
<add key="logfile" value="Log.txt"/>
<!-- Rule Name-->
<add key="RuName" value=""/>
<!-- Set this if you access eBay API server behind a proxy server-->
<add key="Proxy.Host" value =""/>
<add key="Proxy.Port" value =""/>
<!-- set proxy server username/password if necessary-->
<add key="Proxy.Username" value=""/>
<add key="Proxy.Password" value=""/>