CF not finding QT

I'm running AE CS3 on Windows XP SP2. CF installed and registered and was always working perfectly till recently tried. I apply CF to a clip and simplified interface opens and all controls appear to work fine. I try to switch to full interface and get a warning I need an earlier version of QT than I have. I cleaned QT out of PC, reinstalled latest version, verified it works with some mov files. Also verified I could render out a mov file from AE. Also cleaned up PC (registry, broken shortcuts, etc.) Nothing seems to enable the full interface to work. Again, it used to. BTW, also restored the PC to a point 2 weeks ago and all works fine except full interface. Can't find a word in the documentation to help (CF or AE!). Can anyone help? Do I need to reinstall AE itself? Will I have to re-register CF? Thanks.