If you are receiving error messages when you attempt to purchase NCoin, there are a few other payment options you can try. You may want to refer to this link for more details:

http://www.lineage2.com/en/marketplace/buy-ncoin/ 

1. Use a Credit Card
2. Use Paypal
3. Purchase NCoin Cards from your local GameStop
4. Purchase NCoin Cards from Amazon.com
5. If none of these options work, please click here to contact Support.