I am facing the same case, I have no idea ?
If you took the time to search for the thread why don't you read the replies? See here:
I assume you are using a public connection and probably there are some user/s that is using the same connection that got banned from this forum so registering under the same IP will give you proxy ban (evil points IIRC)
If you sign up from a public connection that has already been used and abused then you are required to pay a fee. Just find a IP/connection that is 'fresh' and you can sign up for free.... or just pay the required fee.