Someone recently reported an issue with corrupted version check files. Simply re-installing the game does not necessarily remedy this problem... unless you delete them before installing. Screwy thing with the Windows versioning... newer files are not always automatically overwritten with older ones when you re-install.

The fix was to open the files in notepad and make sure they both show the same version string. Drill into the XIV install folder. There are two subfolders, boot and game. Under each of them, open the .ver files in notepad or other text editor and make sure they are showing the same string. Also double check the .bck files as well---these don't need to be identical, but they should have a version string that follows the same format as the others. Any one of these may have become corrupted, and may even have gotten the "Read Only" attribute set on them. So you may want to right-click them and select "Properties" to make sure they aren't checked as "Read Only" as well.

http://forum.square-enix.com/ffxiv/t...=1#post1894706

This may be an indication that a disk check may be in order. Better to nip the problem in the bud now if your security descriptors are starting to get knackered up (common problem with Windows).