Backup permission issue

I have a WD mybook live and I would like to back it up using crashplan (for the wife)

Crashplan can see the public folder on the mybook but if I tried to point the backup at a private folder it cannot see it.

Crashplan runs under a local system account so it does not prompt me for a user and a password, any way to map a windows user account to the mybook linux users creation screen?

If no way to input the security credentials the backup will not succeed

have to check if crashplan supports backing up private shares?