How about completely uninstalling the program from your system, do a scan for nasties on your computer, do a defrag, a reboot, and then try re-installing it? I've had programs in the past that just wouldn't install until I did this...and I do weekly maintenance of my system. You never know, it could be an out of place digit in the code or any number of 100 different things...could have been a hiccup in the installer too. It's worth a shot anyhow.
Jim