I have never heard of this one but have heard great things about one called Spinrite. Here's a link.

http://grc.com/spinrite.htm

I am a diehard user of Drive Image...great program and wish I had an answer. I know some Seagate drives have "spare" sectors to which data can be relocated if areas go bad. It may be that Drive Image is not able to detect these relocated areas if this is what happened. Drive Image will usually give errors if too many bad sectors are found and will not complete. You might check the web site (now at Symantec, bummer) for information.