I've been having this problem with my Black and White recently, I have the game patched, but for some reason it won't let me run the football addon installer with giving me the error "Sorry, Black and White does not appear to be installed on your system" I get the same error if I try to uninstall the patch.

I'm running XP Pro SP3 and a legitimate, original copy for B&W with legitimate serial, so I can't understand what's going on.

Any help would be appreciated.