Express Vista upgrades are late and error prone
Those who purchased a Windows XP based machine between October 26, 2006 and March 15, 2007 were eligible to get a free upgrade to Vista via the “Express Upgrade” program offered by Microsoft. This program was started to help users that wanted a Vista based machine last year, when Vista was supposed to be released, to get a free upgrade.
The program is now in full swing
, upgrades are coming in late, they are error prone and some serial keys aren’t working.
Full article here: Source