On February 28, Microsoft® will disable Internet activation for all Microsoft Windows® XP product keys located on the Certificates of Authenticity (COA) labels distributed by large, multinational OEMs.
Direct OEMs of Microsoft (large multinational OEMs that that have a direct signed license agreement with Microsoft) usually preinstall Windows software using System Lock Preinstall (SLP), which is a direct OEM's method of legitimately bypassing Product Activation on behalf of their customers.
To reduce the illegal trafficking of these OEM product keys Microsoft will "disable" the ability to activate these direct OEM Product Keys over the Internet. When a customer or reseller tries to activate using a Product Key found on the list of "disabled" Keys, the online product activation wizard will instruct them to call Microsoft where a customer service representative can assist them further.
News source: Aviran's Place
