"0x80070490" Error When Trying to Install Windows Updates

This weekend I was rolling out Microsoft security updates via WSUS, when I noticed a particular server failed to install KB2799494. The error message given was :

Installation Failure: Windows failed to install the following update with error 0x80070490: Security Update for Windows Server 2008 R2 x64 Edition (KB2799494).

I have blogged about this before, but the System Update Readiness Tool can fix various Windows Update errors across versions of Windows from Vista onwards.
I downloaded the correct version of the tool for the OS I was using (Server 2008 R2 x64) and run the update. The tool proceeded to install and run :

System Update Readiness Tool

The tool may take a while to run, and you need to let it complete.  It verifies the integrity of the following :
Files located in

• %SYSTEMROOT%\Servicing\Packages
• %SYSTEMROOT%\WinSxS\Manifests

Registry data located under the following subkeys

• HKEY_LOCAL_MACHINE\Components
• HKEY_LOCAL_MACHINE\Schema
• HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Component Based Servicing

If the tool detects any inconsistencies or incorrect data, it will replace it with a corrected version.