hard disk problems

[Steve Lemke]

Recently, I've been getting the following in my /usr/adm/unix.log:

HDERR ST:51 EF:10 CL:FF80 CH:FF01 SN:FF00 SC:FF02 SDH:FF25 DMACNT:FFFF DCRREG:95 MCRREG:9100 Tue Aug  2 02:00:38 1988

drv:0 part:2 blk:19552 rpts:1 Tue Aug  2 02:00:39 1988

HDERR ST:51 EF:10 CL:FF80 CH:FF01 SN:FF00 SC:FF02 SDH:FF25 DMACNT:FFFF DCRREG:95 MCRREG:9B00 Tue Aug  9 02:01:22 1988

drv:0 part:2 blk:19552 rpts:1 Tue Aug  9 02:01:22 1988

Now, the special thing about 2:00 am is that's when my uucico cron runs
to call another local system.  However, sometimes I force uucico to run
from the keyboard at other times during the day, I get no unix.log
entries.  I don't know why they both happened on Tuesday, as my uucico
cron runs daily.

Can anyone tell me what causes these messages to happen?  They don't 
appear to be "hard" errors (non-recoverable).  Should I add this block
to my bad block table?  How do I go about doing that?

Thanks in advance.

-Todd-