You didn't install it correctly.

Most likely, you put the 'ffxi' folder in the install folder for the game. This means all the data files are in the wrong place. You're actually supposed to copy the *contents* of the ffxi folder, not the folder itself.
In the ffxi install folder, you probabbly have something like this:
\ffxi\
\ROM0\
\ROM1\
\ROM2\
...
and a bunch of files. If you go into the \ffxi\ folder you will see many of the same files and folders.
Just go into the FFXI folder, and move all the stuff in there back into the install folder. Say YES if it asks to overwrite any files.

In short, if you go to where you installed and you see an \ffxi\ folder, you did it wrong.