Session Value Problem after Page load

You can create a class like this:

using System;
using System.Web;

namespace MyWeb
{
    public class AppSession
    {
        public static UserInfo LoginUser
        {
            get
            {
                if (HttpContext.Current.Session["userinfo"] == null)
                {
                    HttpContext.Current.Session["userinfo"] = new UserInfo();
                }
                return (UserInfo)HttpContext.Current.Session["userinfo"];
            }
            set
            {
                // Detect null value
                // Delete this IF ELSE checking if you want to allow a null value to be assigned
                if (value == null)
                {
                    throw new Exception("Value assigned to Session-LoginUser detected.");
                }

                HttpContext.Current.Session["userinfo"] = value;
            }
        }
    }
}

Then you can access it any where in your application:

public partial class WebForm1 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            AppSession.LoginUser = new UserInfo();
            AppSession.LoginUser.ClientID = 1;
            AppSession.LoginUser.SessionID = 1;
            AppSession.LoginUser.ClientName = "Cl1";
            AppSession.LoginUser.UserID = 1;
            AppSession.LoginUser.UserName = "Manas";
        }
    }
}

Then at the second page:

protected void Page_Load(object sender, EventArgs e)
{
    if (AppSession.LoginUser == null)
    {
        Response.Redirect("~/Logout.aspx");
    }
}

Now, go ahead and try again. Whenever there is a null value assigned to AppSession.LoginUser, an Exception will be thrown. From there you can trace where is the error occur in your code.

By the way, this block of code:

Response.Write("<script>");
Response.Write("var height = screen.height;");
Response.Write("var width = screen.width;");
Response.Write("var params='left=0,top=0,height=' + height +',width=' + width + ',resizable=yes,scrollbars=yes,status=yes';");

Can be written as this:

Response.Write(@"

<script type=""text/javascript"">
    var height = screen.height;
    var width = screen.width;
    var params='left=0,top=0,height=' + height +',width=' + width + ',resizable=yes,scrollbars=yes,status=yes';"
                
);

You won't have to repeat Response.Write() for each line.
If you want to escape a double quote symbol

"

you can escape it by typing it twice like this:

""

Another example of using @"":
This code:

xmlString += "<root>";
xmlString += "<username>" + loggedin.UserName + "</username>";
xmlString += "<userid>" + loggedin.UserID + "</userid>";
xmlString += "<hosturl>" + ConfigurationManager.AppSettings["HostURL"] + "</hosturl>";
xmlString += "<serviceurl>" + ConfigurationManager.AppSettings["ServiceURL"] + "</serviceurl>";
xmlString += "<random>" + new System.Random().NextDouble().ToString() + "</random>";
xmlString += "<version>" + ConfigurationManager.AppSettings["TAVersion"] + "</version>";
xmlString += "<sessionid>" + loggedin.SessionID + "</sessionid>";
xmlString += "<clientname>" + loggedin.ClientName + "</clientname>";
xmlString += "<subscriptionid>" + HttpUtility.UrlEncode(loggedin.SubscriptionID) + "</subscriptionid>";
//xmlString += "<auth>" + Request.Cookies["LOOKINGGLASSFORMSAUTH"].Value + "</auth>";
xmlString += "<sess>" + Request.Cookies["ASP.NET_SessionId"].Value + "</sess>";
xmlString += "<currentyear>" + System.DateTime.Now.Year.ToString() + "</currentyear>";
xmlString += "</root>";

Can be written as:

xmlString = @"
<root>
    <username>" + loggedin.UserName + @"</username>
    <userid>" + loggedin.UserID + @"</userid>
    <hosturl>" + ConfigurationManager.AppSettings["HostURL"] + @"</hosturl>
    <serviceurl>" + ConfigurationManager.AppSettings["ServiceURL"] + @"</serviceurl>
    <random>" + new System.Random().NextDouble().ToString() + @"</random>
    <version>" + ConfigurationManager.AppSettings["TAVersion"] + @"</version>
    <sessionid>" + loggedin.SessionID + @"</sessionid>
    <clientname>" + loggedin.ClientName + @"</clientname>
    <subscriptionid>" + HttpUtility.UrlEncode(loggedin.SubscriptionID) + @"</subscriptionid>
    <sess>" + Request.Cookies["ASP.NET_SessionId"].Value + @"</sess>
    <currentyear>" + System.DateTime.Now.Year.ToString() + @"</currentyear>
</root>";

You won't have to repeat "xmlString +=" on each line.

session does not required i dont know this will help you or not

string loggedin = convert.tostring( Session["user"]);

if (loggedin == "")
{
Response.Redirect("Logout.aspx");
}
else
{

clientWidth = "100%";
clientHeight = "100%";

if loggdin is null then you definately have another problems

regards......:)