I attempted to log on to the installation on my laptop and this error did not occur. This appears to have been something that went wrong with the client files on my desktop, as I attempted a file repair two times in a row without doing anything in between, and the same file (SquareEnix\FINAL FANTASY XI\ROM\2\0.DAT) was flagged both times. I am unsure of why this file was corrupted, but I am going to re-install the game on my desktop.

In summary, this is probably not a bug in-game, but rather an issue with my game client that may have been fixed with a re-installation of the game. Sorry for the confusion.