@Elmer, yes I just ran it. It installed Hotfix for Windows (KB947821) and then I used the troubleshooter for Windows update from the site Saltgrass suggested. Then I restarted the computer and it still didn't work. I still got error code 80070490: Windows Update encountered an unknown error. Any more advice?
The error mentioned seems to refer to an access denied situation.
I suppose we need to look at your WindowsUpdate.log in the Windows folder. If you right click it and select send to, compressed (zip) folder, it will allow you to make a .zip file you could attach using the Paperclip.
If you don't want to do that, copy the last 3 or 4 days of events and paste into notepad. Then zip and attach.
If you want to see if you can find a definition for the error number, you can open two different logs and search for the number. It should have a definition next to the number in one of the logs, probably CBS.log.
WindowsUpdate.log and CBS.log in the Windows\Logs\CBS folder. You may have to copy them to the desktop to open but use the find function in Notepad to search.
Edit: I should also ask if the CheckSur.log showed any errors? I also found a better definition at this Microsoft site and the error seems to mean: