Yea I gave my product key and it gave me a error reference code of 715-123130
If that is a genuine retail product key from a Win 7 install disk that you had purchased, then you can contact MS and have them authorize the download, but others have had problems getting the download to work having contacted MS.
I think one of their techs gave the excuse that there must be something wrong with their servers but as this had been the problem for days on end, I think MS could be deliberately obstructive.
The MS Contact Us is to the right of where you enter the product key to be validated.