The bpbkar log won't help you with SQL backups, but you can build up the following logging directories under the netbackup/logs/ directory on the SQL server:
bpcd
bphdb
dbclient
Create those, and then go into the Backup, Archive, and Restore (BAR) gui, still on the SQL server or active SQL node. There go to the file menu -> NetBackup client properties -> troubleshooting tab (on the right hand side). There set the general logging level to 2, the verbose to 5, and the database to 9. Click okay, and then close out of the BAR gui.
Now go ahead and retry the backup.
Do you see the automatic job start?
Do you see the child jobs calling back to the application-backup schedule? Is it these jobs which are failing?
Go ahead and start with that, and then let me know if you get anywhere, what is the job's detailed status reading? Does it report the parent process which is throwing the status 252?
-Sean