1. An enviroment variable happens now and does not need a re-start but a user or system (be careful you don't remove these) could need restarting... yes... please make sure you have some kind of backup plan before mucking about with system ones mate.
2. If you have got any type of anti-virus running that could perhaps be in the way?
3. Also stay away from "C:\ windows" and "C:\ program files" variables