data recovered via error correction code

Running NT 4.0 server, SP6a. A PDC
SCSI HDs with hardware RAID 5

Got this warning in the event viewer:

Event ID: 33
source: Disk

description: Data was recovered using error correction code on device \device\harddisk0\partition2

whatdoes this mean? Do I have a bad HD? Please answer this question only if you are confident of what you are talking about. Thanks.