user.CurrentUser = User.Identity.Name;

lblResult.Text =
//add user Id to session
Session.Add(
Session.Add(
(A)
Response.Redirect(
(B)



string token = "0x" + FormsAuthentication.HashPasswordForStoringInConfigFile("cardnumber.Substring(8,8)", "MD5"); FormsAuthentication.Authenticate(username,password);FormsAuthentication.RedirectFromLoginPage(username,false);FormsAuthentication.SignOut();"yeah!!yeah!!";"UserId", user.Id);"Login", user);"Default.aspx?uId=" + user.getUserId().ToString(),false);

  protected void LoadSecurityQ()
        {
            string myXMLfile = Server.MapPath("~/Data/SecurityQ.xml");
            XmlDocument xmldoc = new XmlDocument();
            xmldoc.Load(myXMLfile);
            XmlNodeList list = xmldoc.GetElementsByTagName("Questions")[0].ChildNodes;
            ddlSecurityQ.Items.Clear();
            for (int i = 0; i < list.Count; i++)
            {
                ddlSecurityQ.Items.Add(new ListItem(list[i].Attributes["name"].Value, list[i].Attributes["value"].Value));
            }
        }

           public static void sendMail1(string subject, string body)
        {
            System.Net.Mail.MailMessage mail = new System.Net.Mail.MailMessage();
            mail.From = new MailAddress("lilyliu719@gmail.com");
            mail.To.Add(new MailAddress("lilyliu719@gmail.com"));
            mail.Subject = subject;
            mail.Body = body;
            mail.IsBodyHtml = true;
            SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
            client.EnableSsl = true;
            client.Credentials = new NetworkCredential("lilyliu719@gmail.com", "");
            client.Send(mail);
        }    

XML and C#

<Questions>
<question>
    <id>0</id>
    <value>0</value>
    <name>Select One</name>
  </question>
  <question>
    <id>1</id>
    <value>1</value>
    <name>What is your favourite movie?</name>
  </question>
  <question>
    <id>2</id>
    <value>2</value>
    <name>What is the city where you were born?</name>
  </question>
  <question>
    <id>3</id>
    <value>3</value>
    <name>What is your high school name?</name>
  </question>
</Questions>

read xml and bind to DropDownList            string myXMLfile = Server.MapPath("~/Data/SecurityQ.xml");
            DataSet ds = new DataSet();
            try
            {
                ds.ReadXml(myXMLfile);
                ddlSecurityQ.DataSource = ds;
                ddlSecurityQ.DataValueField = "value";
                ddlSecurityQ.DataTextField = "name";
                ddlSecurityQ.DataBind();
            }
            catch (Exception ex)
            {
            }

<Questions>
  <question id="0" value="0" name="Select One"></question>
  <question id="1" value="1" name="What is your favourite movie?"></question>
  <question id="2" value="2" name="What is the city where you were born?"></question>
  <question id="3" value="3" name="hat is your high school name?"></question>
</Questions>

 string myXMLfile = Server.MapPath("~/Data/SecurityQ.xml");
            XmlDocument xmldoc = new XmlDocument();
            xmldoc.Load(myXMLfile);
            XmlNodeList list = xmldoc.GetElementsByTagName("Questions")[0].ChildNodes;
            ddlSecurityQ.Items.Clear();
            for (int i = 0; i < list.Count; i++) {
                ddlSecurityQ.Items.Add(new ListItem(list[i].Attributes["name"].Value, list[i].Attributes["value"].Value));
            }  

Validate mutually exclusive text boxes

Solution1
//ASPX <asp:UpdatePanel runat="server">
  <ContentTemplate>
  <asp:TextBox ID="txt1" runat="server" OnTextChanged="TextBoxOnTextChanged"></asp:TextBox>
<asp:RequiredFieldValidator ID="rfvTxt1" runat="server" ControlToValidate="txt1" .....></<asp:RequiredFieldValidator>
<asp:TextBox ID="txt2" runat="server"OnTextChanged="TextBoxOnTextChanged"></asp:TextBox> <asp:RequiredFieldValidator ID="rfvTxt2" runat="server" ControlToValidate="txt2" .....></<asp:RequiredFieldValidator>
<ContentTemplate> </asp:UpdatePanel>

//CS protected void TextBoxOnTextChanged(object sender, EventArgs e) { string SrcTxtId = ((TextBox)sender).ID; switch(SrcTxtId) { case "txt1": rfvTxt2.Enabled = false; case "txt2": rfvTxt1.Enabled = false; } } //Note: This way by default both the validators will be active but as soon as u enter something in textbox1..

Solution2
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script type="text/javascript">
        function ValidateTextBoxes() {
            var TextBox1 = document.getElementById('<%= TextBox1.ClientID %>');
            var TextBox2 = document.getElementById('<%= TextBox2.ClientID %>');
            if (TextBox1.value == "" && TextBox2.value == "") {
                alert('Please enter atleast one value');
                return false;
            }
            if (TextBox1.value != "" && TextBox2.value != "") {
                alert('Please enter only one value');
                return false;
            }
            return true;
        }       
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
    &nbsp;
    <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
    <br />
    <asp:Button ID="Button1" runat="server" Text="Save" OnClick="Button1_Click" OnClientClick=" return ValidateTextBoxes();" />
    </form>
</body>
</html>