一般处理程序（ashx）使用Session

using System;
using System.Collections;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;
//添加下面这句
using System.Web.SessionState;

namespace Web.ashx
{
    /// <summary>
    /// $codebehindclassname$ 的摘要说明
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    //  添加IRequiresSessionState
    public class checkcustomer : IHttpHandler, IRequiresSessionState
    {

        public void ProcessRequest(HttpContext context)
        {
            //context.Session["parameter"]
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}