Re-Registering the Windows Update Client Components
Windows Update are no longer registered or installed on your computer
Some have reported that simply re-registering the MSXML3.DLL seems to fix the problem.
1. Click Start.
2. Choose Run.
3. In the Run box, type: regsvr32 MSXML3.DLL
Press okay
If that hasn't helped you may need to re-registered some more files:
1. Click Start.
2. Choose Run.
3. In the Run box, type (pressing okay after each one) :-
net stop wuauserv
Repeat for the following:
regsvr32 wuapi.dll
regsvr32 wups.dll
regsvr32 wuaueng.dll
regsvr32 wuaueng1.dll
regsvr32 wucltui.dll
regsvr32 wuweb.dll
regsvr32 MSXML3.dll
regsvr32 qmgr.dll
regsvr32 qmgrprxy.dll
regsvr32 jscript.dll
net start wuauserv
To reinstall the Automatic Updates service, follow these steps in this article -
You receive a "Windows Update has encountered an error and cannot display the requested page" error message when you try to install an update
http://support.microsoft.com/kb/883614
If you need to reinstall the ActiveX controls (because they may have become corrupt) follow this article :-
The Windows Update Web site and the Microsoft Update Web site do not scan for updates when you repair a failed installation of Windows XP Service Pack 2 or of Windows XP Service Pack 1
http://support.microsoft.com/kb/916259
If none of the above has assisted, then see:
http://support.microsoft.com/kb/326253
Method 5: Register Windows Update engine files (Includes Vista)