Session state can only be used when enableSessionState.....................

Session state can only be used when enableSessionState is set to true, either in a configuration file or in the Page directive. Please also make sure that System.Web.SessionStateModule or a custom session state module is included in the <configuration>\<system.web>\<httpModules> section in the application configuration.

在网站的Handler.ashx中操作Session会报enableSessionState异常，在webconfig中配置貌似也不行，其实这里只需要

 public class Handler : IHttpHandler, IRequiresSessionState  

实现一下这个接口就行了。