Try going into C: \Program Files\Common Files. Find something along the lines of Installshield, and delete the installer stuff, Windows will remake it. Last time I had a problem with installer, that did the trick. I can't remember the exact directory since I'm on a formatted version of Windows and the dir hasn't been created yet.
P.S. Don't hold me liable if you f' up and delete something important, it worked for me, might not work for you.