I've been getting a lot of emails saying people have been having trouble registering. We recently installed a spam blocker which scans through a database of known spammers. If you are being blocked from registering but are not a spammer, you can go here to check if your username / IP address / email address was used by a spammer.
http://stopforumspam.com/search
And you can go to this page to request a removal from the database:
http://stopforumspam.com/removal
http://stopforumspam.com/search
And you can go to this page to request a removal from the database:
http://stopforumspam.com/removal