error " Record can not insert Error (Object reference not set to an instance of an object.)" ???

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;


namespace WebApp
{
    public partial class CreateMeet : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {   
        }
        protected void Calendar1_SelectionChanged1(object sender, EventArgs e)
        {
            this.TextDate.Text = "" + this.Calendar1.SelectedDate;
        }

        protected void Button1_Click(object sender, EventArgs e)
        {

            if (!this.FileUpload1.HasFile)
            {
                this.lblStatus.Text = "Please select upload file!";
            }
            else
            {
                this.FileUpload1.SaveAs(Server.MapPath("Myfile/" + FileUpload1.FileName));
                this.lblStatus.Text = "<b>" + FileUpload1.FileName + "</b> Uploaded.<br>";

                SqlConnection objConn;
                SqlCommand objCmd;
                String strConnString, strSQL;
 
                strConnString = "Server=localhost;UID=sa;PASSWORD=12345;database=mydatabase;Max Pool Size=400;Connect Timeout=600;";
                objConn = new SqlConnection(strConnString);
                objConn.Open();

                strSQL = "INSERT INTO Createmeet (MeetID,NameMeet,TypeMeet,Date,Time,Location,files) " +
                " VALUES " +
                " ('" + this.TextBoxID.Text + "','" + this.TextNM.Text + "','" + this.DropDownListTypeMeet.SelectedItem + "', " +
                " '" + this.TextDate.Text + "','" + this.DropDownListTime.SelectedItem + "','" + this.DropDownListRM.SelectedItem + "','" + FileUpload1.FileName + "')";

                objCmd = new SqlCommand();
                objCmd.Connection = objConn;
                objCmd.CommandType = CommandType.Text;
                objCmd.CommandText = strSQL;
                objCmd.ExecuteNonQuery();

                objCmd = null;
                objConn.Close();
                objConn = null;

                try
                {
                    objCmd.ExecuteNonQuery();
                    Response.Redirect("ListMeet.aspx");
                }
                catch (Exception ex)
                {
                    this.lblStatus.Visible = true;
                    this.lblStatus.Text = "Record can not insert Error (" + ex.Message + ")";
                }

            }
        }
    }
}