I have downloaded the patch for the Blaster Worm
(KB823980) but am unable to install on XP Professional.
The installation starts, and the dialog box disappears
after 30 seconds or so.

I am also unable to install Security updates from Windows
Update. They download but fail to install. I have the
following error messages in the Windows Update.log -
0x80070080 and 0x80070643.

I have renamed the catroot2 directory, done all the
registry fixes suggested here, deleted the iuctl.dll and
iuengine.dll, but still no luck.

Any ideas??