Try quitting iTunes and restarting it. Then try Genius again.
I found a fix.
Quit iTunes, then Delete the iTunes Library Genius.itdb file in the parent iTunes folder.
When you go back into iTunes, follow the regular procedure to enable Genius and it works.
I'm calling AppleCare in the morning to troubleshoot this.
Finally! It works
Although I noticed that if I had Safari open while I did this it didnt seem to have an effect (might just be something with my Mac though)
Damn it! That was a tough cookie to crack!
Cookies!! Quit iTunes then go to your /user/library folder and move the Cookies folder to the desktop or delete it.
Turn on Genius. It works!
There must be some weird setting saved in cookies with an incorrect URL to send the info to Apple.