If you want the same drives to be mapped each time, use this instead, it prevents getting errors about the local device name being in use.
Put these commands just before your usual drive mapping commands in the script:
net use <drive>: /delete
OR
net use * /delete (This will remove all mappings)
Take out the /persistent option for the usual mapping commands.(since some versions of Windows don't understand it anyways)
I prefer the first command since the users might map other drives on their own, unless you don't want that.