ITNinja

When registration of the engine is corrupted, all attempts to run .msi packages fail.
To correct the registration of the Windows Installer, unregister and then register the Installer service using the command line switches shown below. This shuts down and reregisters the service, which assures that the Windows Installer engine should function properly. Enter the following commands from a command prompt:
msiexec /unregister
msiexec /regserver
If this fails to resolve your problem try performing the following steps:
1) Unregister Windows Installer:
msiexec /unregister
2) Rename the following files from the command prompt: Msi.dll, Msiexec.exe, and Msihnd.dll (by changing the names to msi.dll.bak, msiexec.exe.bak and msind.dll.bak respectively.)
3) Restart Windows.
4) Install the Windows Installer service again (InstMSI.exe). Don't have this? Check here.
Note: when attempting to delete/rename the MSI files Windows File Protection may keep you from being able to do so. One visitor suggests starting Windows in safe mode with a command prompt to deal to the 3 msi files.