Unable to access Windows Update website from Windows XP SP3 KB2497281
I was unable to update a customers Windows XP pc via the web browser but automatic updates worked fine. I thought there was a problem with the disc I had, so I re-installed xp with an original disc but the same problem existed, I recently found an article at: http://social.technet.microsoft.com/Forums/en-US/itproxpsp/thread/7aebba8b-3779-4257-8a21-66828d89da82 where other people were experiencing the same problem, It seems that Microsoft has changed something there end that is stopping updates working via the browser (thanks Microsoft). The fix that worked for me was to re-install Windows Update Agent (WUA) links are provided below.
For x86-based computers (WindowsUpdateAgent20-x86.exe)
For x64-based computers (WindowsUpdateAgent20-x64.exe)