A common error message when trying to reinstall/upgrade a software program (like iTunes etc). Here's a way to avoid getting it:
This message usually means a previous installation of a software is getting in the way of the new installation. It's kinda nutty that this would cause a problem, but we live in a nutty world. The fix is to download a free program from Microsoft that will totally and completely remove the old software. Then the new version can load unimpeded.