invalid operation exception error

comd.ExecuteNonQuery();

protected void Button1_Click(object sender, EventArgs e)
    {
        SqlCommand comd = new SqlCommand("select MT.Reg_id,PR.fname+PR.mname+PR.lname AS Name, CONVERT(varchar(10),PR.DOB,104)as[DD.MM.YYYY],PR.F_H_name,PR.adr_local+PR.adr_po+PR.adr_city+PR.adr_state AS Address,PR.Pincode,ED.exam_10,ED.school_10,ED.Board_10,ED.Yr_pass_10,ED.sub_10,ED.Percent_10,ED.Exam_12,ED.school_12,ED.Board_12,ED.Yr_Pass_12,ED.sub_12,ED.Percent_12,ED.Exam_grad,ED.school_grad,ED.Board_grad,ED.Yr_pass_grad,ED.sub_grad,ED.Percent_grad,ED.Exam_post_grad,ED.school_post_grad,ED.Board_post_grad,ED.Yr_pass_post_grad,ED.sub_post_grad,ED.Percent_post_grad,ED.Exam_phd,ED.school_phd,ED.Board_phd,ED.Yr_pass_phd,ED.sub_post_phd,ED.Percent_phd,ED.Exam_other,ED.school_other,ED.Board_other,ED.Yr_pass_other,ED.sub_post_other,ED.Percent_other,MT.submit_date,CT.Csir_emp,CT.Category,CT.ph,CT.Govt_emp,CT.J_K,CT.exservice,CT.women_cat,JN.bond,JN.Min_time,JN.Max_time,EX.Emp_Name_Addr1,EX.Post1,EX.Date_from1,EX.Date_to1,EX.Perm_temp1,EX.Sal_grade1,EX.Emp_Name_Addr2,EX.Post2,EX.Date_from2,EX.Date_to2,EX.Perm_temp2,EX.Sal_grade2,CN.country_visit,CN.Period_from,CN.Period_to,CN.Purpose,EE.prof_train,EE.Res_exp,EE.List_pub,RF.Ref_name1,RF.Desig1,RF.Lab_inst1,RF.Relation1,RF.Ref_name2,RF.Desig2,RF.Lab_inst2,RF.Relation2 FROM Main_Table1 MT INNER JOIN Category1 CT ON MT.Id=CT.Id INNER JOIN Country1 CN ON CT.Id=CN.Id INNER JOIN Experience1 EX ON CT.Id=EX.iD INNER JOIN Extra_EXP1 EE ON CT.Id=EE.Id INNER JOIN Joining1 JN ON CT.Id=JN.Id INNER JOIN List_enclose1 LE ON CT.Id=LE.Id INNER JOIN Personal1 PR ON CT.Id=PR.Id INNER JOIN Education1 ED ON ED.Id=CT.Id INNER JOIN Refrees1 RF ON RF.Id=MT.ID order by reg_id");
        comd.ExecuteNonQuery();
       
        SqlDataAdapter da = new SqlDataAdapter(comd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }