I have some variable in my DataEntityLayer which are common for all the users for example 

```
public class DataEntityLayer : System.Web.UI.Page
{
    public string UserName
        {
            get
            {
                if (Session["UserName"] == null)
                {
                    GotoLoginPage();
                    return null;
                }
                else
                    return Session["UserName"].ToString();
            }

            set { Session["UserName"] = value; }
        }
}

```

I am using this variable to display Username when a user logs in, this is working fine but goes null frequently. How can I avoid that or let me know a way to declare a variable in my Layer to show Username of a user when he logs in.