一个异常问题（登陆cookie）
客户那边是虚拟机，web登录是用cookie做的，现在出现了一个异常问题，客户端有时候出现无法登陆，检测到cookie是不存在的，重新登陆无反应。但是在服务器内登陆却是正常。这个异常要重启服务器才能恢复正常。
搞不懂什么异常？？？？？？？？？

登陆代码

string username = Request["username"].ToString();

string password = Request["password"].ToString();



//验证数据库用户表

UserModel user = DllFactory.getTrainDll.getUser(username, password);



if (user != null)//通过

{

    HttpCookie aspCookies = new HttpCookie("aspusername");

    HttpCookie aspCookiesPwd = new HttpCookie("password");

    HttpCookie aspCookiesuid = new HttpCookie("uid");

    HttpCookie aspCookiesPower = new HttpCookie("spower");//T代表教师，U代表学生，S代表管理员

    HttpCookie aspCookiesUserID = new HttpCookie("aspuserId");



    aspCookies.Value = Server.UrlEncode(user.UserName.ToString());

    aspCookiesPwd.Value = user.PassWord;

    aspCookiesuid.Value = user.Uid.ToString();

    aspCookiesPower.Value = user.Spower.ToString();

    aspCookiesUserID.Value = user.Uid2;



    aspCookies.Expires = DateTime.Now.AddDays(3);

    aspCookiesPwd.Expires = DateTime.Now.AddDays(3);

    aspCookiesuid.Expires = DateTime.Now.AddDays(3);

    aspCookiesPower.Expires = DateTime.Now.AddDays(3);

    aspCookiesUserID.Expires = DateTime.Now.AddDays(3);



    HttpContext.Current.Response.Cookies.Add(aspCookies);

    HttpContext.Current.Response.Cookies.Add(aspCookiesuid);

    HttpContext.Current.Response.Cookies.Add(aspCookiesPwd);

    HttpContext.Current.Response.Cookies.Add(aspCookiesPower);

    HttpContext.Current.Response.Cookies.Add(aspCookiesUserID);



    Response.Redirect("index.aspx");

}

退出登录代码

HttpCookie cookies = Request.Cookies["aspusername"];

if (cookies != null)

{

    cookies.Expires = System.DateTime.Now.AddDays(-30);

    Response.Cookies.Add(cookies);

}



HttpCookie cookies1 = Request.Cookies["password"];

if (cookies1 != null)

{

    cookies1.Expires = System.DateTime.Now.AddDays(-30);

    Response.Cookies.Add(cookies1);

}



HttpCookie cookies2 = Request.Cookies["uid"];

if (cookies2 != null)

{

    cookies2.Expires = System.DateTime.Now.AddDays(-30);

    Response.Cookies.Add(cookies2);

}



HttpCookie cookies3 = Request.Cookies["spower"];

if (cookies3 != null)

{

    cookies3.Expires = System.DateTime.Now.AddDays(-30);

    Response.Cookies.Add(cookies3);

}



HttpCookie cookies4 = Request.Cookies["aspuserId"];

if (cookies4 != null)

{

    cookies4.Expires = System.DateTime.Now.AddDays(-30);

    Response.Cookies.Add(cookies4);

}