You might have some corrupted files in your FFXIV installation, here is a list of checksums of all files in the FINAL FANTASY XIV folder on my ssd, get a md5 batch checker of your choice (or just grab this one if you don't have any) and let it test your data. If you get any errors then that's most likely your problem.

It could also be your RAM though, so try running it at least twice and check if the error always pop up on same files - if not, then your RAM is dying.