When you go to Windows Update, are you getting an error message stating that
you're using an unsupported version of IE? Several of these are known to
cause that problem:
1) Zone Alarm Pro [Private Header Info - enabled?] Reset "Ad Blocking" and
"Cookie Control" to "medium" "Mobile Code Control" = Off
2) Symantec (ISS\NIS) [Enable Browser Privacy - enabled] Active Content -
"Allow All Scripts To Execute" Problem: some sites cannot detect the 128 bit
encryption Solution: Completely remove and reinstall NIS.
3) Any "ad blocking" software that blocks "http_referer" or contains entries
that are blocking access to the desired site.
4) HOSTS file that contains entries that are blocking access to the desired
site.
5) Cookie blocking software that are blocking "required" Cookies.
6) Pop-up blockers that are stripping header\url info.
7) WebWasher Standard Filter/URL Filter
8) Make sure the following entry is not corrupt:
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet
Settings] "User Agent"="Mozilla/4.0 (compatible; MSIE 6.0; Win32)"
Note: "Win32" = Windows 98\ME Other versions = (compatible; MSIE 6.0;
Windows NT 5.0
(Courtesy of MVP Mike Burgess)