Tip 55: Can’t run a .MSI install?

You try to run a .MSI (Microsoft Installer) package and you can’t because another installation is in progress? After restarting your computer, you receive the same error message?

To clear the previous aborted installation use the registry editor to navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer
and delete the InProgress subkey.