iTunes deauthorization error: 'iTunes is unavailable

Hi, I just purchased a new PC and when I go to authorise for iTunes, it shows that there is more than 5 computers authorised. Two of these are old computers I don't have access to so I try to deauthorise all however it keeps going up with the same error that iTunes is unavailable and to try later. This has been the same the past week. I really need to get everything transferred now! Why can't I deauthorise the old computers?

Cheers

Greg