A little background is needed for this one. I was rebuilding a development server to match updated QA and PROD servers. This is a physical server running Windows 2003 x64. While installing WSS 3.0 February Uber Cumulative update (KB 961766) and Office Servers 2007 February Uber Cumulative update (KB 961576) I received the following error in the upgrade.log file:
[SPIisWebSiteWssSequence] [ERROR] [5/14/2010 10:13:05 AM]: Action 3.0.3.0 of Microsoft.SharePoint.Upgrade.SPIisWebSiteWssSequence failed.
[SPIisWebSiteWssSequence] [ERROR] [5/14/2010 10:13:05 AM]: InstallAspNet 891541206 failed.
[SPIisWebSiteWssSequence] [ERROR] [5/14/2010 10:13:05 AM]: at Microsoft.SharePoint.Upgrade.EnsureAspNetScriptMapInstalled.Upgrade()
at Microsoft.SharePoint.Upgrade.SPActionSequence.Upgrade()
The highlighted number above references an IIS 6.0 site ID, so the error means the patch was unable to work with ASP.NET to modify a particular web application.
This thread helped me understand and fix the error. It seems that particular web application was running in 32-bit mode, where IIS is running in 64-bit mode. I think, more specifically, that ASP.NET was bound to this web application in 32-bit mode and needed to be rebound elsewhere.
The actual fix is to re-register ASP.NET. The key that was missing from other articles I read is that you need to do this from the Framework64 directory on the server. So the fix is actually running this command:
%windir%\Microsoft.NET\Framework64\v2.0.50727\aspnet_regiis –i
Re-running the patches produced a clean upgrade.