Why does iTunes 11 tell me that .msi files are not there....

Why does iTunes 11 tell me that .msi files are not in the correct directories when the previous installer and this one put them there?

I tried to upgrade to the latest iTunes as I have done since the year dot...

iTunes 11 installer is stuffed and I can't even go back to a previous version now... what a stuff up

Philistine_R