But why fails? What error message is thrown?
First of all, try to run the bat manually by double clicking, and see if it works there. Then you can try to automate, but it's easier to go one step at a time.
About permissions, Program Files has read access for every user, and My Documents has read-write for you and nothing for others. So running manually you should be able to do it, provided you have write permissions on the target folder.
Maybe it's a problem caused by running at shutdown. Check under what user context is running the bat in that condition.