When trying to install a SharePoint Cumulative Update I encountered the following error, directly after the update detection:
The detection failed, this can be due to a corrupted installation database
The installation files in the C:\Windows\Installer folder were deleted. These files are required to install updates.
When an application or update of an application is installed, the installation files are stored in the C:\Windows\Installer folder. When another update is installed, the updates checks the Installer folder and retrieves install information and other required components from that folder. So never delete files in the C:\Windows\Installer folder......in our case someone unfortunately did, resulting in the earlier mentioned error :-(
On the MS Forums I found the solution for this issue. Doug Chandler has found out a way of copying the missing files from a working server to the broken server and running the Office Diagnostics tool to fix the issue. The only difference I encountered was that when I ran the Office Diagnostics tool, the tool required the installation packages of SharePoint and all of the language packs. By default it check the same folders as used during installation, so if you have these files in another directory it is going to ask you for the specific folder for all packages (148 in my case).