SBS 2003 R2 Installation Fails

I know, not the ideal Saturday night, right?

When trying to install the SBS 2003 R2 Technologies disc you might see a very descriptive error like this:

Windows Small Business Server Update Services has encountered an error.

The error references a log file at C:\Program Files\Microsoft Integration\Windows Small Business Server 2003\Logs\R2_Setup.log. There's nothing terribly indicative of the problem in that log file either, but you might see some junk like this:

!Error! ForceAllDefaultSettings: An exception occured while configuring Wsus defaults. Information about the exception: System.Runtime.InteropServices.COMException (0×80040154): COM object with CLSID {E9D8E314-5A2C-4FBA-8DF9-C3A038544CB0} is either not valid or not registered. at Microsoft.SBS.UpdateServices.WsusDefaults.WsusConfigurationDefaults.ConfigureComputersForWsusAutomaticUpdates() at Microsoft.SBS.UpdateServices.WsusDefaults.WsusConfigurationDefaults.ForceAllDefaultSettings(Boolean isCleanInstall, Boolean configureAutomaticDownloads)ConfigureUpdateServices: An exception occured while setting WSUS defaults: System.Runtime.InteropServices.COMException (0×80040154): COM object with CLSID {E9D8E314-5A2C-4FBA-8DF9-C3A038544CB0} is either not valid or not registered.
   at Microsoft.SBS.UpdateServices.WsusDefaults.WsusConfigurationDefaults.ConfigureComputersForWsusAutomaticUpdates() at Microsoft.SBS.UpdateServices.WsusDefaults.WsusConfigurationDefaults.ForceAllDefaultSettings(Boolean isCleanInstall, Boolean configureAutomaticDownloads)
   at R2SetupWizard.R2WIConfigureUpdateServices.DoWork(StringDictionary sd)
!Error! WorkItemExecutor: ComponentMessageException occured in DoWork() for work item ConfigureUpdateServices: R2SetupWizard.ComponentMessageException: Exception of type R2SetupWizard.ComponentMessageException was thrown.
   at R2SetupWizard.R2WIConfigureUpdateServices.DoWork(StringDictionary sd)
   at R2SetupWizard.WorkItemExecutor.ExecuteWorkItems(StringDictionary sd, ExecutorCallback beforeWork, ExecutorCallback afterWork)

Now it all makes sense, right? Yeah, didn't help me much either.

The trick here is you need to use the BUILTIN\Administrator account, not some other domain/local admin account that you've created. I imagine you'd probably also have this problem if you're renaming the Administrator account through group policy.