Quicktime won't finish install on Windows 7

I'm running Quicktime 7.7.1 on Windows 7 Pro. Everytime QT 7.7.4 is offered to me by Apple update I try to install it but it never completes for "reason unknown." It suggests that I download and install manually, but that also always fails "unsuccessful." This is probably a minor upgrade, but I've been trying to do it for about six months now and it never completes. I'm just curious as to why? I have the CS6 suite and I know it makes use of quicktime, so I know it's working but why can't I upgrade? Any help would be appreciated.