A lot of people get this problem when trying to get NX through the NX credit system, or when they try to "Get free nx". Well what this is is a security precaution put into place by Nexon a few months back. If your IP address i out of the normal range of the IP first used to buy NX credit, you will not be able to buy, or "get free nx". There is no way to avoid this error. You simply have to find a different way of getting NX.