datetime:Conversion failed when converting date and/or time from character string.

 protected void btnUpDateInterested_Click(object sender, EventArgs e)
        {
                      
            objConn = new SqlConnection(strConnString);
            objConn.Open();
            objCmd = new SqlCommand();
            objCmd.Connection = objConn;

            if (chkIDCardPeople(requestIDCardPeople))
            {
                Boolean countchbListProgram = false;//ตรวจสอบ checklistbox มีการเลือกหรือมไม่

                for (int i = 0; i <= this.chbListProgram.Items.Count - 1; i++)
                {
                    if (this.chbListProgram.Items[i].Selected == true)
                    {
                       countchbListProgram = true;//ตรวจสอบว่ามีการ ใส่ checkbox หรือไม่

                        string itemProject = this.chbListProgram.Items[i].Text;
                        string  itemIndex = this.chbListProgram.Items[i].Value;
                        // Response.Write("<br/>" + itemProject + "Value = " + itemIndex + "<BR/>");

                      string  strSQLFillInterested = "INSERT INTO PeopleProjects(" +
                                "IDCard,ProjectID,CreatedDate,CreatedBy" +
                                ")" +
                                "VALUES ('" + requestIDCardPeople + "'," + itemIndex + ",'"+ DateTime.Now +"','" + Session["UserName"].ToString() + "')";

                        objCmd.CommandText = strSQLFillInterested;
                        objCmd.CommandType = CommandType.Text;

                        try
                        {
                            objCmd.ExecuteNonQuery();
                            //Response.Write("<b><font color='red'>Fill Interested successful</font></b>");
                        }
                        catch (Exception ex)
                        {
                            Response.Write("<b><font color='red'>Fill Interested failed (" + ex.Message + ")</font></b>");
                            return;
                        }
                      
                    }

                }

                if (countchbListProgram)
                {
                    Response.Write("Fill Interested successful");
                    Response.Redirect("ListPeople.aspx");
                }
                else
                {
                    Response.Write("Fill Interested Unsuccessful,Not fill checkbox");
                }

                objConn.Close();
                objConn = null;
                

            }
            else
            {
                //ไม่พบ id card ที่ระบุ
                Response.Write("คุณระบ id card ไม่ถูกต้อง กรุณากลับไปหน้า List People");
                return;
            }
            
 
        }

        private bool chkIDCardPeople(string requestIDCardPeople)
        {
            objConn = new SqlConnection(strConnString);
            objConn.Open();

            SqlDataAdapter objAdapter;
            DataTable dtChk = new DataTable();

            string strSQLchkIDCard = "SELECT * FROM People WHERE IDCard = '" + requestIDCardPeople + "'";

            objAdapter = new SqlDataAdapter(strSQLchkIDCard, objConn);
            objAdapter.Fill(dtChk);

            if (dtChk.Rows.Count > 0)
            {
                return true;

            }
            return false;
            
        }