Click start
Then type run
and copy and paste the following:
%SYSTEMROOT%\SYSTEM32\REGSVR32.EXE %SYSTEMROOT%\SYSTEM32\WUAUENG.DLL
Taken here:
http://answers.microsoft.com/en-us/windows/forum/windows_vista-windows_update/windows-update-error-number0x80070424/95998d7e-9e38-4599-a6cd-fd201447fa92
and I tried it successfully