A checksum error is not a bad block on the harddisk, it is a logical error in the file system. It can be corrected for example by DiskSalv (if the HDD is smaller than 4 GB).
http://aminet.net/package/disk/salv/DiskSalvOr backup / format / restore. You should make a backup anyway. Repairing always has the risk of losing some files or whole directories.
