Kay, I’m sure many of you are familiar with Error 406, it shows up every time we confirm our credit card information when trying to add a monthly subscription to our accounts. It was reported in some cases that 1£/€/$ was charged from their bank account each time the error occurred, therefore be careful with it.

The issue is not at your card or the bank you use, do NOT waste time calling them.
Many of the people affected by this error can’t buy Crysta due country restrictions, cutting quite short our payment options, it makes me wonder if the card issue isn’t also country related, also found this:

I was having a problem renewing my sub. what I had found out was my card was getting region locked incorrectly. I ended up having to set up a VPN and set it to a US IP (even though I'm already in the US). After that, the payment went right through.
@ http://www.reddit.com/r/ffxiv/commen..._subscription/

Warning: Errors were also reported by using Steam Wallet & Game Time cards, can’t confirm if it’s related to the Error 406.

Personally won’t try to subscribe until this issue is fixed to avoid further problems, but if you have any extra information about this error that you would like to share, please do.