You need to clear your cookies in Internet Explorer (even if you don't use it for web browsing). This must be done manually, or using a 3rdparty software to ensure all cookies are actually removed (the auto-removal tool built into IE doesn't actually remove everything). If you still have problems after that, lower your security settings. If you prefer to have high-security in IE, here is a step by step guide to playing FF14 with high security in IE.

http://forum.square-enix.com/ffxiv/t...nal-Fantasy-14