It could easily be an unrecoverable error on the drive or perhaps its out of replacement sectors for remapping purposes. But I've had and have seen that problem you're having and it only seems to come around during very large, long transfers. I remember making a registry change to XP SP1 way back when and fixing it with one particular drive.
If tweaks dont fix it, before I threw it out, I'd pull the drive, hook it up to an IDE controller, repartition it and do a low level format on it, then put it back in the external case. Might solve it.
Be fearful when others are greedy, and greedy when others are fearful. Just another form of "buy low, sell high" for those who have trouble with things. This rule is not universal. Do not buy a 1973 Pinto because everyone else is afraid of it.