I just installed tbackup from 4psa for Plesk. It installed fine and the licence was installed without a problem. However, every time I tried to set it up, it said that the directory that the backups were to be saved to didn't exist.
Problem was that the debs are for 32-bit systems and the system is 64-bit. A helpful tech from 4psa kindly informed me that the ia32-libs package needed installing.