FreeBSD 8.2 command 'zpool status -x' with error

  pool: poolusb
 state: ONLINE
status: One or more devices has experienced an error resulting in data
        corruption.  Applications may be affected.
action: Restore the file in question if possible.  Otherwise restore the
        entire pool from backup.
   see: http://www.sun.com/msg/ZFS-8000-8A
 scrub: scrub completed after 0h2m with 0 errors on Wed Nov 16 03:06:44 2011
config:

        NAME             STATE     READ WRITE CKSUM
        poolusb          ONLINE       0     0     0
          mirror         ONLINE       0     0     0
            gpt/SMI      ONLINE       0     0     0
            gpt/SANDISK  ONLINE       0     0     0

errors: 1 data errors, use '-v' for a list