The "banned ip" error typically occurs when the IP address that is being passed during the verification step is not the user's IP. When a request comes in from the user's browser (on your site) to our systems for a Solve Media Puzzle, the IP address of that challenge request is logged. Subsequently, when you validate that particular challenge, you also send us the same end user's IP. This allows us to confirm that the person answering the puzzle is the same person requesting it.
A "banned ip" error would result if we see activity on your site such as various IPs making the challenge request, and only a small set of IPs being used over and over on the verification step.
To our fraud system, it looks like someone is trying to break into your site by bypassing our security, perhaps by outsourcing CAPTCHA solving to a 3rd party. This is usually caused by a reverse proxy.
To fix this, you need to pass the user IP to the verification step. If the problem is a reverse proxy, this can typically be accomplished by sending the value of the 'HTTP-X-FORWARDED-FOR' header.