I am not sure it will works for you or not but I always use following code to get connection string..
protected string ConnectionString
{
get
{
return WebConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
}
}
using (var connection = new SqlConnection(ConnectionString))
{
connection.Open();
----------body----------
connection.close();
}
Wherever you want connection string in web form use connection variable.