Windows XP Professional will have been on sale for so long that the software will run out of product activation keys without an update, Microsoft's official system builder blog has revealed. As the Professional edition has had its lifecycle extended to the end of January 2009 -- over seven years after its initial October 2001 release -- the software developers have found that the existing keys would not cover sales until the end of the period, requiring a fix for new customers to use the software. Known as Service Pack 2c, the update will be mandatory for computer makers by September as future PCs might not be able to install XP as soon as this fall, Microsoft says.

Other versions of Windows XP such as Home, Media Center, Tablet, and 64-bit Professional will not be affected as they will either be removed from the market earlier or have a separate key range.

The change reflects the problems encountered by the long-delayed release of Windows Vista, which is said to have been hurt by XP as its familiarity for developers and users has forced the company to extend support past previous cutoff dates. System designers such as Dell have also been forced to restore XP options on some of their computers in response to complaints about poorly-written Vista drivers and a distaste for the new Windows update.