Give this a try and see if it solves the problem.........
Go to Start>Run and key in each of these commands, one at a time, clickingon OK or hitting ENTER after each command and then clicking on OK in theRegSvr32 dialogue box:
regsvr32 softpub.dll
regsvr32 mssip32.dll
regsvr32 initpki.dll
regsvr32 wintrust.dll
Restart and see if you can now successfully use Windows Update site.