Check Condition on CDB: 0x28

I'm running NetBSD 3.0/sparc64 on a SUN Ultra1.
The machine is more than 10 years old but still doing it's job.
Once in a while I have the following errors (not very often as
you can see).

What does it mean? Should I worry?
It this my disk wearing out?

Regards,
Thierry.

May 23 03:15:57 vega /netbsd: sd0(esp0:0:0:0):  Check Condition on CDB: 0x28 
00 00 31 5f 84 00 00 04 00
May 23 03:15:57 vega /netbsd: SENSE KEY:  Recovered Error
May 23 03:15:57 vega /netbsd: INFO FIELD:  3235717
May 23 03:15:57 vega /netbsd: ASC/ASCQ:  ID CRC Or ECC Error
May 23 03:15:57 vega /netbsd: FRU CODE:  0xd7
May 23 03:15:57 vega /netbsd: SKSV:  Actual Retry Count: 1

May 31 03:17:53 vega /netbsd: sd0(esp0:0:0:0):  Check Condition on CDB: 0x28 
00 00 30 a5 20 00 00 20 00
May 31 03:17:53 vega /netbsd: SENSE KEY:  Recovered Error
May 31 03:17:53 vega /netbsd: INFO FIELD:  3188021
May 31 03:17:53 vega /netbsd: ASC/ASCQ:  ID CRC Or ECC Error
May 31 03:17:53 vega /netbsd: FRU CODE:  0xd7
May 31 03:17:53 vega /netbsd: SKSV:  Actual Retry Count: 1

Dec 12 03:20:31 vega /netbsd: sd0(esp0:0:0:0):  Check Condition on CDB: 0x28 
00 00 35 fc 20 00 00 20 00
Dec 12 03:20:31 vega /netbsd: SENSE KEY:  Recovered Error
Dec 12 03:20:31 vega /netbsd: INFO FIELD:  3537970
Dec 12 03:20:31 vega /netbsd: ASC/ASCQ:  ID CRC Or ECC Error
Dec 12 03:20:31 vega /netbsd: FRU CODE:  0xd7
Dec 12 03:20:31 vega /netbsd: SKSV:  Actual Retry Count: 1