Hello!

One of my friends is trying to re-install the game since it somehow it got royally screwed up, but whenever he tries to install, he gets this error:

CRC error: The file C:\Program Files\Square Enix\FINAL FANTASY XIV\data\5B\20\00\00.DAT doesn't match the file in the setup's .cab file. The medium from which you are running the setup may be corrupted; contact your software vendor.

He was able to successfully install the game once before, so does anyone have any idea what the heck this error means?