I would say you are right. Live regions are to show changing information on screen, hence "live". If there was AJAX, there would be a good case for an alert to say what went wrong. However, with a full post back to the server, I'd say it wouldn't be effective here.
I just tried this with NVDA on Firefox, it does (surprisingly) read the alert out as soon as the page is opened. However, you need to decide if this is the functionality you'd be going for.
Hope this helps.