general backup/flexbackup help

I have an sme5.1.2 server with a seagate scorpion 40 tape drive (SCSI).

I would like to do a full backup of a certain directory (and all files and dirs underneath it) on thursdays and incremental backups of the same directory every other weekday.
I looked into it and figured I would just setup a cron job to do "flexbackup -fs all" for the full backup (I changed fs from the default). and for the incremental I would do "flexbackup -fs all -level 9"

but when I do that it says: Only level 0 dumps are allowed on a subdirectory

What is a solution to my situation?

Thanks,
Max