Backup Exec uses the System Logon Account to connect to the target folder

1. Verify that the Backup Exec services are running under the same account as the System Logon Account

(Backup Exec Console ->Settings icon upper left -> Configuration and Settings -> Logon accounts -> Manage Logon Accounts, to verify System Logon Account )

2. Add this Account to NAS Local Administrator Group.  Also add this account to share permissions of the folder to be backed up.

3.Try adding NAS Device with Name and IP Address both in User Defined Selections.