The problem is that a site with "www." functions as an entirely different site as one without "www." in the front. So, since this is the issue causing the error in your case, it doesn't have access to the user data because they have gone to a different site.
Once you fix that problem, then the failure page should go to the same site and the form data would be accessible so you could add it to an email and send it to yourself.
First fix the www. issue like I referenced above and then you probably won't even have any errors to report.