I'm having problems with Windows update in that it wont install a particular security patch.

The exact same patch appears each day, and I download it. I receive no error messages to say that it hasnt installed, but the next day (after a restart) the same patch still needs to be downloaded.

The only time it tells me that it hasnt been installed is when I try installing from the windows update program, rather than just when the bubble pops up in the bottom right of the screen.

Any ideas?