On most drives this is easy enough to fix using the --debug option and adding it to the database, but some drives out there are still not readable even with this option. The net is littered with posts about drives that can't be identified by either hddtemp or even hdparm -i, giving the error...

HDIO_GET_IDENTITY failed for '/dev/sd[x]': Invalid argument

Fortunately these drives can be identified by both smartctl and even udev ata_id, but that doesn't help you read the temp with hddtemp for use in scripts and monitoring tools that rely on hddtemp.

I realize this software has been abandoned, but maybe one day someone will pick up the torch and update the drive detection routines. If I had the chops to do it myself I would. Until then I will have to use a special smartctl script just for my one problem drive. (WD30EZRX-00MMMB0)

sudo smartctl -a /dev/sd[x] | awk '/Temperature/ {print $10}'