Most likely:
http://windowshelp.microsoft.com/Windows/en-US/Help/bc1393cf-9f9c-79c7-0f91-9337c2c412341033.mspx
Ignore the error number as it is different for everyone.
This error may occur if the date and time on your computer varies too much
from the valid date and time of the SSL certificates that are used by the
Windows Update Web site. This causes the scan process to fail. Make sure
that you verify that the time and date are accurate on your computer.
NOTE: If you have a firewall, you need to ensure Port 123 is open to
synchronize with internet time.
Less likely:
This does not work for everyone:
1: Open up "Control Panel" and navigate your way to "Programs and Features".
2: Click "View installed updates" on the left hand side.
3: Find the update KB929777 and uninstall it.
4: Attempt to install the update again in Windows Update
5: Once successful, restart your PC.
If you are still having problems:
Are you running x64 or x86?
Do you have SLI graphics, or more than one GPU on your video card?