You may be prompted to activate Windows Vista on a computer on which Windows Vista activation was not previously required. Although this problem rarely occurs, it may occur during typical use of a Windows Vista-based computer. For example, this problem may occur under one or more of the following conditions: You install a device driver. You install a program. You run a new program. You remove a program. This problem may occur because a specific system setting is removed when a program runs with administrative credentials. The removal of this system setting may cause a BIOS validation check to fail. The BIOS validation check is part of the system activation process. Therefore, you may be prompted to activate Windows Vista, even though the system did not previously require activation. For example, this problem is known to occur when you use Intuit QuickBooks 2007. However, this problem may also infrequently occur when you install other programs or device drivers. More and download fix at Microsoft