A confusing (but harmless) hotfix error message

If you've tried to install this week's two performance and compatibility hotfix rollups for Windows Vista, you may have encountered an odd error message. I've got the explanation, plus instructions on how to verify that the updates have indeed been correctly installed.

If you’ve tried to install the two new Windows Vista update packages Microsoft released this week (938979:Windows Vista Performance Update and 938194: Windows Vista Reliability Update), you may have encountered this odd error message:

Windows Vista update package error message

What’s the deal?

Simple. The update doesn’t apply to your system because you already installed these updates. The beta versions, as it turns out, are identical to the final released versions. You can see for yourself by computing the checksum values for each one:

windows6.0-kb938194-x86.msu afa984ba13f9703609ba0e8fd0b36879

windows6.0-kb938979-x86.msu 2e8d8eea28fba080e95730669484fc82

When you double-click the newly downloaded update, the Windows Update Standalone Installer checks your system, sees that it’s already been installed, and throws this misleading dialog box at you.

If you want to verify that the update is installed, go to Control Panel and click View Installed Updates, under Programs and Features heading. Each update has a KB number at the end of its name; look for KB938979 and KB938194.