Per a Google research project a few years ago, the lack of negative S.M.A.R.T. indicators is not a good indication of hard drive health. A hard drive can have no indicators at all and fail. That's not really applicable, though, as you have a negative indicator. I'm inclined to agree with Al on the possible source, because the other possible source for that indicator is a severe controller or drive bearing problem.
That said, have you tried running chkdsk on all your drives? You'll also find some information on some of the causes of file conflicts in this FAQ.
I'm not on the WHS team, I just post a lot. :)