An exception of type Microsoft.SharePoint.PostSetupConfiguration.PostSetupConfigurationTaskException was thrown while applying MOSS service packs

I was building out a new medium farm the other day and applying the various SharePoint updates, when I received the following error after installing the Infrastructure Updates and running the Config wizard:
“An exception of type Microsoft.SharePoint.PostSetupConfiguration.PostSetupConfigurationTaskException was thrown. Additional exception information: Failed to upgrade SharePoint Products and Technologies.”
Going through my log files, I realized the exception was being thrown for the following reason:
“The access control list on C:\Program Files\Common Files\Microsoft Shared\Web server extensions\12\template\layouts\Web.config could not be modified because the path could not be located in the file system.”
After a few Google searches, I found the solution in the “Deploy software updates for Office SharePoint Server 2007” article on TechNet (go figure). The reason this was happening was because my farm still didn’t have any Web Apps provisioned so the Web.config file which was supposed to be in the 12\template\Layouts folder was missing.

To resolve this, simply copy the Web.config file in the 12\Config folder and paste it into your 12\templates\Layouts. Now run the Config wizard again and everything should work smoothly.

Hope this helps!!