installing FFxi onto an external HDFollow

Hello,
ok so recently the PC i have been playin on has had some issues where POL viewer would be laggy and and the screens would overlap each other. so i figured i would just un-install the viewer and re-install it. well after it was un-installed now i recieve error messages and it wont install. i dont really mind because i have the game on 360 also. so i had a 20 gig external HD around and decided to install FFxi to it. and bring it to work. (yes i have the luxury of playin at work...but not enough to play just sell stuff on AH and bazaar) so i brought it to work and it wont play. i dont remember the exact error message i got but something along the lines of the files do not exist...but i just installed them. i checked the HD and they are there. so i took it home booted it from the HD and it ran fine. is there some kind of safeguard on FFxi that doesnt allow you to play the game this way?
Thanks for any advice.

Thanks Pawkeshup



would there be anyway to fix this?