code 643 error while installing KB951847

Failed 5 times, and could not find the error code explanation on Microsoft
web site.
Please help. Thanks in advance.

Search KB95184
<http://www.microsoft.com/communities/newsgroups/en-us/default.aspx?query=KB951847&dg=microsoft.public.windowsupdate&cat=en_US_56d1dd45-de9e-4fc5-9bc1-2d1d0de6daee&lang=en&cr=US&pt=&catlist=&dglist=&ptlist=&exp=&sloc=en-us>

1. Write down the .NET Framework versions which are already installed:

How to determine which versions of the .NET Framework are installed and
whether service packs have been applied
http://support.microsoft.com/kb/318785

2. Now see Resolutions Methods 1 or 2 in
http://support.microsoft.com/kb/923100. After running the
appropriate/needed tool, (re)install all .NET Framework versions manually
using the download links on the page.

Try setting up these 2 steps first, before you restart your computer, then
reinstall KB951847

Step (1) Turn on your ORIGINAL Window Firewall
Go to Control Panel -->Security Center -->under Window Firewall, Turn it ON.
the original Window Firewall must be TURNED ON....

(Do not let your Antivirus/Internet Security took control of the Firewall)

Step(2) Turn Off any HTTP or Web Scan
Ensure that your antivirus/Internet Security software DID NOT SCAN WEB(http)
Traffic

My own experience:
I failed twice installing it, as a result my laptop(Vista Premium) failed to
restart.
Not untill it go through a Start-Up Repair before system was restored back
to normal.

I finally got mine to install after 7 failed attempts...here's what I did.
1. go to http://support.microsoft.com/default.aspx/kb/290301
2. download and install the utility
3. use it to uninstall the installation files for all of your .NET
Frameworks listed when you run the program(1.1, 2.0, 3.0, 3.5 e.g.). GOOD
NEWS...this program just removes the installation files which are causing the
error code #643, NOT the actual frameworks installed so you won't need to
re-download them :-)
4.*optional- clean your registry(I did)
5. reboot your computer
6. now install KB951847... you'll actually see the installation progress bar
move!!!

KB951847 caused also trouble on my system. I tried a couple of things,
including the removal of the Software Distribution directory (after stopping
the Windows update Service), uninstall all .NET versions,...) with no result.
I finally reinstalled a clean Windows Vista and then the update passed. The
whole exercise took me the better part of a day.

System: Windows Vista Business (upgrade from XP).

I presume that upgrading from XP to Vista, rather than a clean install,
caused the issue.

Most experts recommend against using registry cleaners.