Export to Text file Error: Object reference not set to an instance in ASP.Net

I am exporting to text file.While exporting,i am getting this error "Object reference not set to an instance"

dt.Load(reader);//error

here i am getting the error as object reference not set to an instance of an object

private DataTable dataTblForRetrieveInTextFile()
        {
            DataTable dt = new DataTable();
            SqlConnection conn = null;
            dt = null;
            try
            {
                Int64 currCat = Convert.ToInt64(cmbCategories.SelectedValue);
                Int64 status = Convert.ToInt64(cmbAllStatus.SelectedValue);
                Int64 country = Convert.ToInt64(cmbAllCountries.SelectedValue);
                Int64 region = Convert.ToInt64(cmbRegions.SelectedValue);
                string frmDate = dateTimePicker1.Value.ToString("MM-dd-yyyy");
                string toDate = dateTimePicker2.Value.ToString("MM-dd-yyyy");

                Int64 user = Convert.ToInt64(cmbUsers.SelectedValue);
                string isDateSelected = Convert.ToString(dateTimePicker1.Checked);
                string isRemovesSelected = checkBoxRemoves.Checked.ToString();
                string isKeywordSelected = checkBoxKeywords.Checked.ToString();
                string isDomainSelected = checkBoxDomain.Checked.ToString();
                int isActive = 0;
                string logfield = "";
                if (chkApproved.Checked)
                {
                    isActive = 1;
                }
                else
                {
                    isActive = 0;
                }

                if (cmbCategories.SelectedIndex != -1)
                {
                    logfield = cmbCategories.Text;
                }
                if (cmbAllStatus.SelectedIndex != -1)
                {
                    logfield = logfield + "," + cmbAllStatus.Text;
                }
                if (cmbUsers.SelectedIndex != -1)
                {
                    logfield = logfield + "," + cmbUsers.Text;
                }
                if (cmbAllCountries.SelectedIndex != -1)
                {
                    logfield = logfield + "," + cmbAllCountries.Text;
                }
                if (cmbRegions.SelectedIndex != -1)
                {
                    logfield = logfield + "," + cmbRegions.Text;
                }
                if (frmDate != toDate)
                {
                    logfield = logfield + "," + frmDate;
                }
                if (toDate != "")
                {
                    logfield = logfield + "," + toDate;
                }
                if (chkApproved.Checked == true)
                {
                    logfield = logfield + "," + "Approved checked";
                }

                if (checkBoxKeywords.Checked == true)
                {
                    logfield = logfield + "," + "Keywords checked";
                }
                if (checkBoxRemoves.Checked == true)
                {
                    logfield = logfield + "," + "Removes checked";
                }
                if (checkBoxDomain.Checked == true)
                {
                    logfield = logfield + "," + "Domain checked";
                }

                string todaydate = DateTime.Today.ToString("MM-dd-yyyy");
                string time = DateTime.Now.ToString("h:mm:ss tt");

                MyConnect myCnn = new MyConnect(); String connString = myCnn.getConnect().ToString();


                SqlCommand command;

                conn = new SqlConnection(connString);
                command = new SqlCommand();

                conn.Open();
                command.Connection = conn;


                command.CommandType = CommandType.StoredProcedure;

                command.CommandText = "GetDataForTextFile1";

                command.Parameters.AddWithValue("@currCat", currCat);
                command.Parameters.AddWithValue("@fromdate", frmDate);
                command.Parameters.AddWithValue("@todate", toDate);
                command.Parameters.AddWithValue("@user", user);
                command.Parameters.AddWithValue("@country", country);
                command.Parameters.AddWithValue("@region", region);
                command.Parameters.AddWithValue("@status", status);
                command.Parameters.AddWithValue("@isDateSelected", isDateSelected);
                command.Parameters.AddWithValue("@isRemovesSelected", isRemovesSelected);
                command.Parameters.AddWithValue("@keyword", isKeywordSelected);
                command.Parameters.AddWithValue("@domain", isDomainSelected);
                command.Parameters.AddWithValue("@active", isActive);


                SqlDataReader reader = command.ExecuteReader();
                dt.Load(reader);//error
                string count = dt.Rows.Count.ToString();
                conn.Close();
                //for log
                SqlCommand command11;
                command11 = new SqlCommand("insert into userlogexport(user_id,date,time,filter,count,Export_page,fileType) values('" + currentLoggedUserId + "','" + todaydate + "','" + time + "','" + logfield + "','" + count + "','retrieve_Data','Text')", conn);
                conn.Open();
                command11.ExecuteNonQuery();
                conn.Close();

                //command11.Connection = conn;

                //command11.CommandType = CommandType.StoredProcedure;             
                //command11.CommandText = "savelogdetails";

                //string ipAddress = Request.ServerVariables["REMOTE_ADDR"];
                string message = "";

                // message = "Ip Address: " + ipAddress;
                message = message + "\n User Name: " + uName + "\n";
                message = message + "\n Date: " + todaydate + "  Time:" + time + "\n";
                message = message + "\n filters:" + logfield + "\n";
                message = message + "\n Rows count:" + count + "\n";
                message = message + "\n FileType: text";
                sendEmail("mahi@expogr.com", "Database Export report-Retrive Data", "db@expofairs.net", message);


            }
            catch (Exception e1)
            {

            }
            finally
            {
                if (conn.State == ConnectionState.Open)
                    conn.Close();
            }
            return dt;
        } 

return value:0

result:emailids