ASP.NET C#: I am loosing session value after a few postbacks!

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C#

ASP.NET

I have a funny issue with my asp.net c# website. The problem only comes when i upload the solution online, it just works fine when I am running on local machine.

Basically, i have a normal login page where I take username and password via text boxes, match it against the db and upon validity, I set up some session variables

(Session["user_in"])

and navigate user to default.aspx page.

On this default.aspx page under

page_load 

event, I have following code

if (!IsPostBack)
        {
            if ((Session["user_in"] != "Y"))
            {
                Response.Redirect("~/Login.aspx");
            }
           
        }

And on this default.aspx page, I am reading from db and writing to db.

But annoyingly after a few postback, i get signed out to

Login.aspx

page.

And the only code on the page that does that is under if condition in page_load event, meaning that it cannot find the value of

(Session["user_in"])

.

This only happens when i upload solution to the server, local machine doesn't behave that way.

Any ideas, help please?