connection strings in web.config

What am I doing wrong?

This works:

SQLConn.ConnectionString = "Data Source=McD_DB;Initial Catalog=McDFeelGood;User ID=uuu;Password=ppp"

Now I want to put it in my web.config, but these don't work ("ConnectionString property has not been initialized"):

SQLConn.ConnectionString = ConfigurationSettings.AppSettings("McDFeelGoodConnectionString")(VS IDE says this method is obsolete)
SQLConn.ConnectionString = System.Configuration.ConfigurationManager.AppSettings("McDFeelGoodConnectionString")

<connectionStrings>
<add name="McDFeelGoodConnectionString" connectionString="Data Source=McD_DB;Initial Catalog=McDFeelGood;Persist Security Info=True;User ID=uuu;Password=ppp" providerName="System.Data.SqlClient" />
</connectionStrings>

OK well this worked:

<appSettings>
<add key="McDFeelGoodConnectionString" value="Data Source=McD_DB;Initial Catalog=McDFeelGood;Persist Security Info=True ;ID=uuu;Password=ppp" />
</appSettings>