Now SQL Azure is available for commercial use only and CTP has ended in December of 2009. So no promo code is now accepted even if you got it before 1January2010 from Microsoft. If you are interested in using Azure Services then head over to www.microsoft.com/windowsazure for purchase information. This is the reason all valid promo code are also not working complaining that code is already used.
However I believe it would have been nicer if Microsoft displayed this update instead of only telling “Code is already used” while rejecting the Promo codes.