Engel- are you using Microsoft Update or Windows Update?
If you are on Microsoft Update, you can try reverting to Windows Update,
restarting, and doing a scan and download under Windows Update. You may
then be able to go back to Microsoft Update with success.
The option to revert to Windows Update is in the left column under "Change
Settings"--wait for the page to load and scroll all the way down.
This prescription has worked for me in some cases on XP--I'm not sure
whether it'll do the same on Vista, but it is easy to try.
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