Web (ASP.NET), C# -> Update ไม่ได้แค่ค่าเดียว งงมากไม่ทราบสาเหตุ ช่วยทีครับผม

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
using System.Web.Configuration;
using System.Web.Mail;

namespace WebApplication1
{
    public partial class WebForm5 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ReEmeetingConnectionString"].ConnectionString);
            con.Open();
            //string cmdStr = "SELECT * FROM members WHERE username ='" + Session["id"] +"'";
            string cmdStr = "SELECT * FROM members WHERE member_id ='" + Session["id"] + "'";
            SqlCommand cmdd = new SqlCommand(cmdStr, con);
            SqlDataReader objReader = cmdd.ExecuteReader();

            while (objReader.Read())
            {
                txtName.Text = objReader.GetString(1);
                txtLastName.Text = objReader.GetString(2);
                txtinstitution.Text = objReader.GetString(3);
                txtPosition.Text = objReader.GetString(4);
                txtTel.Text = objReader.GetString(5);
                txtEmail.Text = objReader.GetString(6);


            }

            objReader.Close();
            con.Close();
        }

        protected void btnRegister_Click(object sender, EventArgs e)
        {
                
                SqlCommand objCmd = new SqlCommand();
                String strSQL;

                SqlConnection objConn = new SqlConnection(ConfigurationManager.ConnectionStrings["ReEmeetingConnectionString"].ConnectionString);
                objConn.Open();


                if (this.FileUpload1.HasFile)
                {
                    this.FileUpload1.SaveAs(Server.MapPath("Myfiles/" + FileUpload1.FileName));
                 
                    //this.lblText.Text = "<b>" + FileUpload1.FileName + "</b> Uploaded.<br>";

                    strSQL = "UPDATE members SET " +
                    " firstname = '" + txtName.Text + "' " +
                    " ,lastname = '" + txtLastName.Text + "' " +
                    " ,institution = '" + txtinstitution.Text + "' " +
                    " ,position = '" + txtPosition.Text + "' " +
                    " ,telephone = '" + txtTel.Text + "' " +
                    " ,email = '" + txtEmail.Text + "' " +
                    " ,picture = '" + FileUpload1.FileName + "' " +
                    " WHERE member_id ='" + Session["id"] + "'";

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


                    objConn.Close();

                    
                }
                else
                {
                    strSQL = "UPDATE members SET " +
                    " firstname = '" + this.txtName.Text + "' " +
                    " ,lastname = '" + this.txtLastName.Text + "' " +
                    " ,institution = '" + this.txtinstitution.Text + "' " +
                    " ,position = '" + this.txtPosition.Text + "' " +
                    " ,telephone = '" + this.txtTel.Text + "' " +
                    " ,email = '" + this.txtEmail.Text + "' " +
                    " ,picture = '" + "null" + "' " +
                    " WHERE member_id ='" + Session["id"] + "'";

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


                    objConn.Close();
                }

                
        }
    }
}