void Application_Error(object sender, EventArgs e)
   {
    //get reference to the source of the exception chain
   Exception ex = Server.GetLastError().GetBaseException();
   //log the details of the exception and page state to the
   //Windows 2000 Event Log
   GUI.MailClass objMail = new GUI.MailClass();
   string strError = "MESSAGE: " + ex.Message + "<br><br><br>" + "SOURCE: " + ex.Source + "<br>FORM: " + Request.Form.ToString() + "<br>QUERYSTRING: " +    Request.QueryString.ToString() + "<br>TARGETSITE: " + ex.TargetSite + "<br>STACKTRACE: " + ex.StackTrace;
if (System.Web.HttpContext.Current.Session["trCustomerEmail"] != null)
{
    strError = "Customer Email : " + Session["trCustomerEmail"].ToString() +"<br />"+ strError;
}
  //Call a method to send the error details as an Email
   objMail.sendMail("test@gmail.com", "myid@gmail.com", "Error in " + Request.Form.ToString(), strError, 2);

strError = System.Web.HttpContext.Current.Session["trCustomerEmail"]

if (HttpContext.Current != null &&
    HttpContext.Current.Session != null) {
  strError = HttpContext.Current.Session["trCustomerEmail"]
}

HttpContext context = ((HttpApplication)sender).Context;

context.Request.QueryString.ToString()
context.Session["key"] = "fasfaasf";