Create a new user defined selection "\\ipaddress-of-archiver"
Create a new logon account. Username "smb" which is the default unchangeable account name. Log in to the Barracuda and under Advanced>Backup set the password. Make sure to set this same password for the logon account in Backup Exec.
Create a new Backup Selection list. Right-click the Barracuda MA object under user defined selection, and click Connect As.. and specify the logon account previously created. You should now be able to drill down to the correct share (typically BMA-SMB), and select it for backup.
Create a new job or policy as appropriate. Note that in the job settings, doing a credential test will FAIL out, but if you start the backup job it should run properly.