Try granting yourself access to their contacts folder under c:\Users with the TakeOwnership script available in our
Freeware DB's File & Folder section. That should take care of the access denied at which point you should be able to script the backup.
Simply install the TakeOwnership script then open Windows Explorer to each directory for which you need permissions and right-click, then choose TakeOwnership from the context menu.
Note: If you Take Ownership of their entire user folder the script might run 15-30 minutes so if it will let you get to it you really just need the Contacts folder under their logins.