Web Forms :: Session_Start Executes Again After An Error Occurs (when Going To Custom Error Page)

I'm having a wicked time trying to redirect the different error scenarios to a custom error page. Basically, I have put some code in Application_Error in global.asax, and done the necessary web.config settings to use Custom Errors.

In global.asax on Application_Error, I stored the Server.GetLastError in Session. The reason I have to store it in Session is because (as far as I know) you lose the exception when using "ResponseRedirect". And the reason I have to use ResponseRedirect is because I am using an UpdatePanel with AJAX calls, and any exception during the AJAX call shows up as a JavaScript error, and doesn't get handled using the custom error page (see this post).

void Application_Error(object sender, EventArgs e){ ////must perform this check to avoid the "Session state is not available in this context" errors if (HttpContext.Current.Session != null) { Session["LastException"] = Server.GetLastError(); } else { // (I think this happens when there are compile-time errors) Server.Transfer("~/Oops.aspx"); }}void Session_Start(object sender, EventArgs e){ //must perform this check to avoid the "Session state is not available in this context" errors if (HttpContext.Current.Session != null) { //initialize the session (http://forums.asp.net/t/1405077.aspx) Session["LastException"] = ""; }}