After seemingly successfully installing Service Pack 2, I can no longer
download upgrades or Windows Update or Windows Defender.

I have stop wuauserv, regsrved everything, deleted datastore, checked
extensively for bots/viruses etc, removed my firewall tried without,
reinstalled and tried with another firewall, installed and ran
Windows6.0-KB947821-v5-x86.

No joy, no change still message Windows Update Encountered an Unknown Error
Code 0x80248011. This error arrived with my update to Service pack 2, all
signs point to this install as causing the problem. Help please.

Make sure to clear your IE cache, and I would go ahead and rename the whole
SoftwareDistribution folder.

-Eddie

How do I reset Windows Update components?
http://support.microsoft.com/default.aspx/kb/971058

What anti-virus application or security suite is installed and is your
subscription current?  What anti-spyware applications (other than Defender)?
What third-party firewall (if any)?  Were any of these applications running
in the background when you installed SP2?

Has a(another) Norton or McAfee application ever been installed on this
machine (e.g., a free-trial version that came preinstalled when you bought
it)?

Free unlimited installation and compatibility support is available for
Windows Vista, but only for Service Pack 2 (SP2). This support for Windows
Vista Service Pack 2 (SP2) is valid until November 26, 2009. Availability of
chat or e-mail support differs depending on your geographic location. Go to
http://support.microsoft.com/oas/default.aspx?prid=13014&gprid=582034 &
select appropriate category (i.e., Download issue; Installation issue;
**Issues after you install a service pack**).
--
~Robear Dyer (PA Bear)
MS MVP-IE, Mail, Security, Windows Client - since 2002
www.banthecheck.com