HttpHandler gets 'Object reference not set to an instance of an object' when trying to access session vars.

If you are using the default, InProc session state, the session vars will be lost each time the aspnet process recycles. This may be your problem, if you post your code, I will try it on my machine to see if it works for me. are you able to use session variables on other pages.?

while this KB alert isn't necessarily your problem, it may give you something to go on, to investigate the aspnet worker process...
http://www.kbalertz.com/kb_841557.aspx

Here is the code to the HTTP handler

namespace FileHandler
{
    //By directory file security
    public class SecureFileHandler : System.Web.SessionState.IRequiresSessionState, IHttpHandler
    {

        //Contructor
        public SecureFileHandler()
        {
        }

        //IHttpHandler Interface
        //Process Request
        public void ProcessRequest(System.Web.HttpContext context)
        {
            //These lines cause an error
            context.Response.Write(context.Session["GoodLogin"].ToString());
            context.Response.Write(System.Web.HttpContext.Current.Session["GoodLogin"].ToString());
           
            //This line causes no error
            context.Response.Write("Test");
        }

        //IsReusable Var
        public bool IsReusable
        {
            get
            {
                 return true;
            }
        }
    }
}

Thankyou for your help.  The reson that it wasnt working was because the session vars had expired without me relizing it, now it works. Thanks again.