Found this trawling around Reddit, worth trying, worked for me.

It's not ideal, but if you want to play the game delete your FFXIV_BOOT.cfg from My Games/FINAL FANTASY XIV - A Realm Reborn.
When you reload the launcher, you'll have to accept the terms, and click the "I already have a Square Enix account" button. At this point you'll be presented with the login form that's on the lodestone which is currently still working, afterwhich you'll be presented with the play button.
Signed - A guy who just spent 2 and a half hours trying to solve a problem that doesn't exist on his computer and only just saw the thread with other people experiencing this. ><
http://www.reddit.com/r/ffxiv/commen...ble_to_access/