I had the same problem today and I have found the solution with a kind of trick. Do this;
Just copy everything in “C:\Program Files\Common Files\InstallShield” from a good working XP PC into the same path of the PC with that problem and start the uninstall process again and see it is working. At least it worked fine with me.
Still I don’t know anything about the source of problem but what I know is right now that it is gone. 🙂