http://support.microsoft.com/kb/949104 Be sure that your trun off your antivirus before you start getting service pack. After you are all done with SP update, turn your antivirus on. For the future, make it a practice to do mirror-image backup on a regular basis so that you have a good working o.s. to get back to if a disaster hits or if your system becomes unsteady. Solution You need to manually install: .NET framework 2 Service Pack 3 for Windows XP If the problem persist, Open your browser and search for: WindowsUpdateAgent30-x86.exe - Microsoft Download the Windows Update Agent. Save the download to your C drive or desktop Click Start, then click Run. Type C: \ WindowsUpdateAgent30-x86.exe / wuforce then click OK to install the WU agent. Restart the computer and try to update.