I ran into this issue as well. I went to the download center and manually pulled the update down. When I attempted to install it, it returned a message stating that it was not applicable to my system so apparently this update is not needed even thought Windows Update thinks it is.
You probably downloaded the wrong flavor. This update has a download for x86, x64 and also a separate one for Server 2k8.
Doesn't matter though ... still wont install, even with the correct download.