提示必须声明标量变量 dataset()

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace datagridview
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string flagpack = "3";
            SqlConnection conn = new SqlConnection(@"server = 192.168.1.159;database =testdb;UID=sa;PWD=062455xzy");
            string sqlPack = "select top 1* from dbo.Table_1 Where flag=@GrdFlag order by id desc";
            SqlCommand cmd = new SqlCommand(sqlPack, conn);

            SqlParameter parameterGridFlag = new SqlParameter("@GrdFlag", SqlDbType.NVarChar);
            parameterGridFlag.Value = flagpack;
            cmd.Parameters.Add(parameterGridFlag);

            try
            {
                conn.Open();
                SqlDataAdapter da = new SqlDataAdapter(sqlPack, conn);
                DataSet ds = new DataSet();
                da.Fill(ds);
                conn.Close();

                ////查询的数据显示到datagridview
                string grdPackTime = ds.Tables[0].Rows[0]["functime"].ToString();
                string grdBatch = ds.Tables[0].Rows[0]["batch"].ToString();
                string grdSoftWare = ds.Tables[0].Rows[0]["software"].ToString();
                string grdClientName = ds.Tables[0].Rows[0]["clientname"].ToString();
                string grdSerialNo = ds.Tables[0].Rows[0]["serialno"].ToString();
                string grdImei = ds.Tables[0].Rows[0]["imei"].ToString();
                string grdModuleSn = ds.Tables[0].Rows[0]["modulesn"].ToString();
                string grdflag = ds.Tables[0].Rows[0]["flag"].ToString();
                string grdBox = ds.Tables[0].Rows[0]["box"].ToString();
                string[] row = { grdPackTime, grdBatch, grdSoftWare, grdClientName, grdSerialNo, grdImei, grdModuleSn, grdflag, grdBox };

                ////给dataGridViewScan控件添加数据
                dataGridViewPack.Rows.Add(row);
                ////datagridview显示排序-降序
                this.dataGridViewPack.Sort(this.dataGridViewPack.Columns[0], ListSortDirection.Descending);
            }
            catch(SqlException ex)
            {
                MessageBox.Show(ex.Message + ex.StackTrace, "Exception Details");
                conn.Close();
            }
            finally
            {
                conn.Close();
            }
        }
    }
}

简单的功能，就是把MSsql查到的数据输入到datagridview显示，但是一直提示“必须声明标量变量@GrdFlag”，可已经声明了,谢谢