AUTOMATIC WINDOWS UPDATE INSTALLATION.
Windows XP SP2 checks at shutdown for any Windows Updates have been downloaded and not installed, then offers to install them as part of the shutdown process. Understandably, this can cause a very slow shutdown on that one occassion and, if something goes wrong, can even hang shutdown completely. To see if your shutdown problem is caused by this issue, look for error 0x80248011 in any of the Windows Update log files, particularly %windir%\SoftwareDistribution\ReportingEvents.log. If present, this indicates a corrupt local metadata store for Windows Update. SOLUTION: Click Start, click Run, type SERVICES.MSC, click OK. Stop the Automatic Updates service. Rename the c:\Windows\SoftwareDistribution folder to c:\Windows\SoftwareDistribution.old. Restart the Automatic Updates service.