I am unable to send mail by selecting all the check boxes.

Question

Dear sir 
I want to send a mail on button click event , After selection of all check box together.

I have putted this code mentioned below(took some help from your site' article also).
but still it throws the error:
 System.NullReferenceException: Object reference not set to an instance of an object.

Source Error: 

Line 447: Line 448: Line 449: string a = GridView1.SelectedRow.Cells[2].Text; Line 450: Session["a"] = a.ToString(); Line 451:


and my code is
protected void Button1_Click(object sender, EventArgs e) { // StringBuilder object StringBuilder str = new StringBuilder(); // Select the checkboxes from the GridView control for (int i = 0; i < GridView1.Rows.Count; i++) { GridViewRow row = GridView1.Rows[i]; bool isChecked = ((CheckBox)row.FindControl("chkSelect")).Checked; //chkSelect.Checked = Convert.ToBoolean(Session["a"]); if (isChecked) { // Column 2 is the Hoarding_ID column str.Append(GridView1.Rows[i].Cells[0].Text); } } // prints out the result Response.Write(str.ToString()); if (GridView1.SelectedRow.Cells[0].Text != null && GridView1.SelectedValue) { string a = GridView1.SelectedRow.Cells[2].Text; Session["a"] = a.ToString(); } con.Open(); SqlDataAdapter da = new SqlDataAdapter("select email_id from Hoarding_buyers where username = '" + Session["b"].ToString() + "'", con); DataSet ds = new DataSet(); da.Fill(ds); DataTable dt = ds.Tables[0]; con.Close(); if (Session["b"] != null) { System.Web.Mail.MailMessage objMM = new System.Web.Mail.MailMessage(); objMM.To = dt.Rows[0][0].ToString(); objMM.From = "[email protected]"; objMM.BodyFormat = System.Web.Mail.MailFormat.Text; objMM.Priority = System.Web.Mail.MailPriority.High; objMM.Subject = "HoardingIndia"; objMM.Body = "Dear Sir/Madam,\r\n\r\n" + "Thank You for Contacting Us. \r\n" + "Our Marketing Team will contact you soon.\r\n\r\n" + "Thanks & regards \r\n" + "Hoardingindia.co.in \r\n" + "011-22239165, [phone] \r\n\r\n"; objMM.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserver"] = "smtp.gmail.com"; objMM.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserverport"] = 465; objMM.Fields["http://schemas.microsoft.com/cdo/configuration/sendusing"] = 2; objMM.Fields["http://schemas.microsoft.com/cdo/configuration/smtpauthenticate"] = 1; objMM.Fields["http://schemas.microsoft.com/cdo/configuration/sendusername"] = "hoardingindia2012"; objMM.Fields["http://schemas.microsoft.com/cdo/configuration/sendpassword"] = "hoardingindia2012"; objMM.Fields["http://schemas.microsoft.com/cdo/configuration/smtpusessl"] = true; System.Web.Mail.SmtpMail.SmtpServer = "smtp.gmail.com"; System.Web.Mail.SmtpMail.Send(objMM); con.Open(); SqlDataAdapter da1 = new SqlDataAdapter("select * from Hoarding_buyers where username = '" + Session["b"].ToString() + "'", con); DataSet ds1 = new DataSet(); da1.Fill(ds1); DataTable dt1 = ds1.Tables[0]; con.Close(); con.Open(); SqlDataAdapter da2 = new SqlDataAdapter("select * from providers_post where h_id = '" + Session["a"].ToString() + "'", con); DataSet ds2 = new DataSet(); da2.Fill(ds2); DataTable dt2 = ds2.Tables[0]; con.Close(); con.Open(); SqlDataAdapter da3 = new SqlDataAdapter("select * from providers where provider_user_name in (select Provider_user_name from providers_post where h_id = '" + Session["a"].ToString() + "')", con); DataSet ds3 = new DataSet(); da3.Fill(ds3); DataTable dt3 = ds3.Tables[0]; con.Close(); System.Web.Mail.MailMessage objMM1 = new System.Web.Mail.MailMessage(); objMM1.To = "[email protected]"; objMM1.From = "[email protected]"; objMM1.BodyFormat = System.Web.Mail.MailFormat.Text; objMM1.Priority = System.Web.Mail.MailPriority.High; objMM1.Subject = "HoardingIndia"; objMM1.Body = "Dear Sir/Madam,\r\n\r\n" + "We have received the details from hoarding buyer. \r\n\r\n" + "Name :" + dt1.Rows[0][1].ToString() + "\r\n" + "Email :" + dt1.Rows[0][10].ToString() + "\r\n" + "Contact No.:" + dt1.Rows[0][3].ToString() + "\r\n\r\n" + "-----------------------------------------------------------------------" + "\r\n\r\n" + "Following are the hoarding details. \r\n\r\n" + "Hoarding ID:" + Session["a"].ToString() + "\r\n\r\n" + "Address :" + dt2.Rows[0][1].ToString() + "\r\n" + "LandMark :" + dt2.Rows[0][6].ToString() + "\r\n" + "State :" + dt2.Rows[0][4].ToString() + "\r\n" + "District :" + dt2.Rows[0][5].ToString() + "\r\n" + "Pin Code :" + dt2.Rows[0][8].ToString() + "\r\n" + "Size :" + dt2.Rows[0][3].ToString() + "\r\n" + "From Date:" + dt2.Rows[0][9].ToString() + "\r\n" + "To Date :" + dt2.Rows[0][14].ToString() + "\r\n\r\n" + "Hoarding Type:" + dt2.Rows[0][11].ToString() + "\r\n" + "Lighting Type :" + dt2.Rows[0][15].ToString() + "\r\n" + "Hoarding Cost:" + dt2.Rows[0][7].ToString() + "\r\n\r\n" + "-----------------------------------------------------------------------" + "\r\n\r\n" + "Following are the Hoarding owner's details in which buyer is intereated: \r\n\r\n" + "Name :" + dt3.Rows[0][1].ToString() + "\r\n" + "Email Id :" + dt3.Rows[0][6].ToString() + "\r\n" + "Contact No.: " + dt3.Rows[0][2].ToString() + "\r\n\r\n\r\n"; objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserver"] = "smtp.gmail.com"; objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserverport"] = 465; objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/sendusing"] = 2; objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/smtpauthenticate"] = 1; objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/sendusername"] = "hoardingindia2012"; objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/sendpassword"] = "hoardingindia2012"; objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/smtpusessl"] = true; System.Web.Mail.SmtpMail.SmtpServer = "smtp.gmail.com"; System.Web.Mail.SmtpMail.Send(objMM1); //Response.Write("<script>alert('Thank you,we will contact you soon.')</script>"); Response.Redirect("search.aspx"); } }