Session state created while response flushed....

[Kasic Slobodan]

Session state has created a session id, but cannot save it because the response was already flushed by the application.

I have a big problem with this error. Few days ago, web app worked fine and when session expired and I refreshed the page, code inside Session_Start in global.asax logs me in again.

            cookie = Request.Cookies\["Userword"\];
            
            if (cookie != null)
            {
                string strCookie = cookie.Value;

                if (strCookie != "")
                {
                    sin.AutoLogin(cookie.Values\["heavy"\],
                        cookie.Values\["metal"\],
                        true, Request.UrlReferrer.AbsoluteUri == null ? "" : Request.UrlReferrer.AbsoluteUri, false);

                }
            }
            else
            {
                if (Session\["UserInfo"\] == null)
                {
                    Response.Redirect("login.aspx");
                }
            }

Yesterday I can't login by refreshing the page, any more. If I login manually, everything is ok. Error raises only when session expires and user refreshes the page. When I try to step in AutoLogin function, try catch block catches the Object reference error before debugger was able to step into a function. The above error I caught in Application_Error in global.asax. I have searched the net for solution, but with no luck. Most of the answers were that you shouldn't use Response.Flush and I have Response.Flush only in captcha class which is loaded on login.aspx page and everything worked great until yesterday. Can anyone help me with this issue?