There is one user in our group for whom our entire SilverStripe-driven website is broken -- both our Production and Staging environments. This user gets a 404, Not Found error on every page. (The 404 page is the pretty SilverStripe 404 page, however, so *something* must be working correctly.) For the rest of us, there are no problems anywhere. For this user, all other websites work correctly, both internal and external. I've already checked his hosts files, dns, etc, and there is nothing unusual.

I am very worried that this is not just one user, however... it's one out of about 10 people that I know of, so it's possible that it's other people out in the public. It started about a week ago -- and we have not changed our production site at all during this time (that I know of.)

One thing that has happened at about the same time is that we installed the Forum module in our sandbox, and this user registered there. Maybe clearing cookies would fix him, but -- that's not enough comfort for me; I want to know *why* this is happening.

Any thoughts? Anyone else ever have these issues?

OK now it's 2 users and I'm starting to panic. For each user, it is only on one browser -- the browser they were using to test the forum module. I just halted all work on our forum dev/rollout, as I can't risk this in production.

BTW we have tried ?isDev=1, build/flush, etc. In all cases the same response with no action taken, as if it cannot interpret anything in the url following the domain.

Would be great if this could be reproduced (ok, maybe not great, but useful) If it happens in 20% of cases, that should be possible..

A couple of questions that I hope might help...

Could it be a conflict with some other custom module?
Did you actually find out if clearing cookies works, as a first step?
Did the user register at the forums?
If so - at the time this happened, was the account still active?
Were any settings changed in between?
Had they possibly created more then one account from the same browser?
After uninstalling the forums, was the site accessible again?
If not - then after setting the database back to the situation before the forums, was the site accessible again?
Could the user reproduce the problem after a new install of the forum?