missing a directive or namespace

I'm using the dataAdapter as you see in the code below.  I'm using VS 2005.  what does the error; The type or namespace name 'SqlDataAdapter' could not be found (are you missing a using directive or an assembly reference?)      mean?

 string strConn = "Database=adventureworks;User ID=se;Password=steve";
            string sqlstr = "select * from production.productcategory";
            using(SqlDataAdapter AWdataadapter = new SqlDataAdapter(strConn,sqlstr));   ****
            DataTable table = new DataTable();
            table.Locale = System.Globalization.CultureInfo.InvariantCulture;
            AWdataadapter.Fill(table);
            dbBindSource.DataSource(table);
            dataGridView1.AutoResizeColumn(DataGridViewAutoSizeColumnMode.AllCellsExceptHeader);
            dataGridView1.DataSource(dbBindSource);