[CentOS] smartd and smartctl

A few weeks ago, one of my servers started complaining, via smartd, that
one drive had one unreadable sector. I umounted it, and ran an fsck -c,
then remounted it. Error didn't go away. Now, what's really annoying is
that I've gotten back to it today, and it's reporting the problem, as it
has for weeks now, every half an hour.

However, when I run
> smartctl -q errorsonly -H -l selftest -l error /dev/sdb
it gives me *nothing*. Anyone understand why I get two different results?

     mark "and I am waiting for the smartctl -t long /dev/sdb to complete"