When going to the Windows Update Web site located at
http://windowsupdate.microsoft.com, the page immediately redirects you to
http://v4.windowsupdate.microsoft.com/en/thanks.asp, which says "you must be running a
Microsoft Windows operating system in order to use Windows Update." This occurs if both a third party firewall and the built-in Windows XP firewall are enabled at the same time.
Please delete the following registry key. Be sure to export this key to a safe location first.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\User Agent\Post Platform
This may be resolved by uninstalling the third party firewall.
The system administrator may have made changes to your corporate firewall/proxy that will not allow Windows Update to operate properly. Please contact your system administrator and have them identify Windows Update as an excluded site on the firewall/proxy.