Hello! We had blocked your IP address temporarily due to its participation in a DDoS attack against us. I've unblocked it for you, and you should now be able to request certificates.
If your system's IP address just recently changed to its current one, then the problem was with the previous holder of that IP.
Otherwise, please check your system carefully: the system, or a site on it, may have been compromised and used to attack others, including us.