Just now, an important bug while registering new forums was discovered.
We've overlooked a small mistake, where the server wouldn't turn forum name to lowercase. So, if you registered a forum with at least one uppercase character, your forum would show 404 (because the Nginx config hostname would break, as there can't be uppercase characters in domain name).
I've patched this for all new forums, and also fixed all previously registered forums affected by this & re-send their administrators a confirmation E-mail. We apologize for the inconvenience.