No se ha inicializado la propiedad ConnectionString. = The ConnectionString property is not initialized.

How can I resolved this matter in VB 2010?

I am running "chat.aspx" file. 

I have write a ConnectionString for my SQL DataBase "LoquitoChat.mdf" in Web.Config file. 

<add name="LoquitoChatConnectionString" connectionString="Data Source=(local);Initial Catalog=LoquitoChat;Integrated Security=True" providerName="System.Data.SqlClient" />

foreach(LobbyInfo lobby in ChatApi.GetLobbyInfoArray()) 

Thanks,