Update failed for Microsoft SQL Server 2008 R2 Service Pack 1 (KB2528583)

I'm attempting to install SQL Server 2008 R2 SP1 64 bit.  I am running Windows 7, 64 bit.  I already have SQL Server 2008 R2 64 bit installed on my system.

1) First I tried via Windows Update.  I'm already caught up on all other required and all other desired optional updates.  When I try to run this update, it fails with this message:

Code 84BC051B Windows Update encountered an unknown error.

When I click "Get help with this error" and "Open the Windows Update Troubleshooter", and progress through the troubleshooter, then it claims to fix something ("Repair Windows Update components - Fixed" and tells me to retry the update, and when I simply click to Try Again,  it says "Windows is up to date - There are no updates available for your computer".

But then if I click to find updates online, it still finds the update for SQL Server R2 SP1 among the available optional updates.

2) Second, I tried downloading an executable to install.  When I run the executable, I get this error:

"SQLServer2008SP1-KB968369-x64-ENU.exe is not a valid Win32 application"

Any idea what is going on?

Thanks!