Dmanager中显示没有为命令对象设置命令是要怎么改鸭？

大佬们，我在用Visual Studio 2012做一个网上商城的新闻管理系统时，不知道哪一步出现错误，运行后总显示什么没有为对象设置命令，请问这种情况要怎么改啊？

Dbmanager的完整代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Configuration;
using System.Data.OleDb;
using System.Data;

/// <summary>
/// DbManager 的摘要说明
/// </summary>
public class DbManager
{
    public DbManager()
    {
        //
        // TODO: 在此处添加构造函数逻辑
        //
    }
    public static int ExecuteNonQuery(string strSQL)
    {
        string constr = ConfigurationManager.ConnectionStrings["accessConn"].ConnectionString;
        OleDbConnection conn = new OleDbConnection(constr);//
        conn.Open();
        try
        {
            OleDbCommand cmd = new OleDbCommand(strSQL, conn);
            return (cmd.ExecuteNonQuery());
        }
        finally
        {
            if (conn.State == ConnectionState.Open)
                conn.Close();
        }

    }
    public static DataTable ExecuteQuery(string strSQL)
    {
        string constr = ConfigurationManager.ConnectionStrings["accessConn"].ConnectionString;
        OleDbConnection conn = new OleDbConnection(constr);//
        conn.Open();
        try
        {
            OleDbDataAdapter adp = new OleDbDataAdapter(strSQL, conn);
            DataSet ds = new DataSet();
            adp.Fill(ds);
            return ds.Tables[0];
        }
        finally
        {
            if (conn.State == ConnectionState.Open)
                conn.Close();
        }
    }
}

求赐教orz