The Windows Installer cache folder is a hidden system folder located at C:\Windows\Installer. Whenever you install a software using the Windows Installer, a copy of changed system information is placed in this folder. The Windows Installer cache contains the saved copies of the installed updates that are applied by the Installer.
This information is required, should you later decide to uninstall the software. This information is stored, not in the form of complete files, but simply as a triggering MSI. If you delete the particular files or folder, you probably would not be able to uninstall or repair or even update the program using the Windows Installer. That is why one should never delete the contents of the Windows Installer folder.
But if you do face a situation where you find that you are unable to uninstall, repair, or update some software, even when you have not deleted any files from the cache, it may be possible that Windows Installer cache folder may have been compromised or corrupted. For instance. Windows Installer will clean-out the installer cache if ever the owner on the %WINDIR%\Installer directory changes from SYSTEM or Administrators.
If you think of copying the missing installer files from some other computer to this one, it will not help, as the files from the cache are unique for every system.
Windows Installer Cache Verifier Package
The Windows Installer Cache Verifier Package troubleshooter can perform automated diagnostic analysis to identify solutions and find if you are missing Windows Installer Cache files.
To run the troubleshooter, visit Microsoft Fix it Center Pro and sign in using your Microsoft Account. You will see a list of Analysis packages. Search for and click on Windows Installer Cache Verifier Package. Give your Analysis Session a name and click Save. You will need this name to be able to see the analysis later on.
Follow the on-screen instructions to download and run the Windows Installer Cache Verifier Package.
Once done, go here after an hour or so, to view the analysis results.
Look for the name you gave for your Analysis Session and check if any of the possible recommended solutions help you.
Missing Windows Installer Cache files
Microsoft Support or third-party software will not really be able to help you recover the missing files from the Windows Installer cache. You may have to reinstall the software or maybe even have to rebuild the operating system, using system restore points, system backups – or even reinstall the operating system.
There are other system error messages that can arise as a consequence of missing Windows Installer Cache files. You can read more about them at KB2667628.
UPDATE: 5th Feb 2017. You can use this PowerShell script “Restore-InstallerFiles.ps1” to scan for the missing Installer files and to restore them from different sources such as the Local folder, Shared folder or another machine which can be accessed from the target machine. It is available on TechNet.