State Management :: Using Application_Error For Redirection / Application_Error To Redirect The User To A Custom Error Page?

I am trying to use the Application_Error to redirect the user to a custom error page. I know I could use the web.config to do this, but let's assume for now that this is not a desirable path to take.

Initially, I tried to do a Response.Redirect to perform this, however, there seem to be occasions where the current http context does not define the response object. So, I attempted to perform a check to make sure that the response object is not null prior to attempting the redirection, and if it is not defined, perform a Server.Transfer instead.

What happens is that in most cases, the Redirect causes the browser to some generic "friendlyish" error page rather than the requested error page.

So then I tried using Server.Transfer exclusively, and this worked well for most cases, however, sometimes the transfer didn't seem to take in the browser. Changing it back to a redirect in these cases solved that problem, but reintroduced the issue where the errors previously being captured and transferred now were being redirected.

What I surmised from this is that in certain contexts where the Application_Error method is trapped, it is necessary to use Server.Transfer in redirection, whereas in others, it is necessary to use Response.Redirect. The question then became twofold: (a) When is one necessary and when is the other? and (b) What available information can I poll to tell me when a given condition exists.

After much searching, I cannot find a reasonable answer to this question. So I began to trap errors and examine the HttpContext object for some indicator. One thing that I was looking for is the reason why if even with a defined Response in the current context does a redirect fail. The only thing that stood out is that even though a Response object may exist, the Session data could be absent. I added the case to check whether the Session data was null and perform a Transfer in this case and it
seems to be handling it properly.

I emphasize "seems to be handling it properly" because no documentation I've been able to find confirms either the problem I am having or whether this is an appropriate strategy for solving it.

I guess the question is, am I on the right track here or is the null Session object just a red herring, indicative of nothing relevant. Here's the check I have set up for reference.

[Code]....