Pb With SQLConnection

 Hi

I would like to have some help for my problem.
I'm trying to retreive the connectionString "MyConnectionString" from app.config using method 1 or 2 to get a connection to my DB (without any success.)
 
--> Partial code
public SqlConnection GetConnection()
        {
            // reference to System.Configuration Library is done
           
        1    SqlConnection Connection = new SqlConnection(ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString);
--> thrown NullReferenceException on   Conn.Open();
           
        2    SqlConnection Connection = new SqlConnection(ConfigurationSettings.AppSettings["MyConnectionString"]);
--> thrown InvalidOperationException ConnectionString not initialised
            return Connection;
        }

       public Contest GetContestFromDB()
        {
            SqlConnection Conn = GetConnection();
            Conn.Open(); ->> thrown Exception 1 or 2...

Here my app.config :
<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <appSettings>
    <clear/>
    <add key="MyConnectionString" value="Server=.SQLExpress;AttachDbFilename=D:Documents and Settings
0xMesdocumentsApp_DataShopperDB.MDF;Database=ShopperDB.MDF;Trusted_Connection=Yes;"></add>
  </appSettings>

  <connectionStrings>
    <clear/>   --> using <clear/> to avoid to load from machine.config
    <add name="MyConnectionString" connectionString="Server=.SQLExpress;AttachDbFilename=D:Documents and Settings
0xMes documentsApp_DataShopperDB.MDF;Database=ShopperDB.MDF;Trusted_Connection=Yes;"></add>
  </connectionStrings>
</configuration>

 
I'm using Visual Studio 2008 with SQLServer 2005 Express Embedded and WindowsXP SP2 .

Have you got any idea ?
I'm not able to sleep anymore...
And I've test this code in ASP.net with the same ConnectionString in the web.config file and it works !!
I'm lost.

By the way, thx if ou get an answer 

ww4ss