After downloading an update for the latest version of Itunes, I keep getting a message saying 'Windows Installer Service' could not be accessed. I have checked that the Windows Installer is running and that I am not in 'Safe Mode'. Often (but not always) the Installer shuts down some time during the download. I have tried with Installer set to Manual and also to Auto but I still keep getting the same message. Any help would be much appreciated.