Error in Data adapter

DataSet ds = new DataSet();
       string selectSql = "Items.Description, Items.ItemNo, Items.Qty FROM Items INNER JOIN  ItemParent ON Items.DoNumber = ItemParent.DoNumber";
       string connectionString = ConfigurationManager.ConnectionStrings["InvoiceConnectionString"].ConnectionString;
       SqlConnection conn = new SqlConnection(connectionString);
       SqlDataAdapter da = new SqlDataAdapter(selectSql,conn);
       da.Fill(ds,"Items");
       PrintGv.DataSource = ds.Tables["Items"];