You're not the only one getting this, Freddy.
Lately we've had people logging in using Proxies. A Proxy is a method used to connect to the internet anonymously. That is, instead of using our own internet connection to access the 'net directly, you're accessing a proxy server, and it piggybacks your connection to the Internet, thus masking your true internet identity.
This forum has been having people logging in using Proxy Servers for a while. While I did not care, we've had dubious accounts (spambots mostly) creating accounts and accessing the forum through proxies, which is why we had that big Chinese Spambot attack a few weeks back.
You're looking at the result of security measures installed. I installed them.
My guess is that you're accessing the internet through one or more of these proxy servers instead of directly, when you connect from your home connection (or you have a Satellite-based Internet connection and its ISP has been identify as one that has allowed spambot accounts in the past). That, or your computer's connection has been hijacked and you need to get your PC looked at.
Talk to whomever is charge of your internet connection, or tell me more details about it via PM (IP address, provider name, etc.). It's likely that the provider or your PC has been accessing a proxy service and has been blacklisted.
EDIT:
I have it now so that you can temporarily still post and view the forum, but not register. Already-created accounts should be able to post (I'm not too happy about that, but there do seem to be active members who are connecting this way).
I really suggest to the few people who are having this problem, to check your internet connection. Are you using a hilariously old browser? Are you piggybacking through a Proxy? Maybe you're accessing stuff through a cellphone connection in a foreign country, or satellite internet may be the issue. In any case, it's in your best interests to find that info out for yourself.