Frank & Mark,
No, I was using neither Digital ICE nor SRD (though I was using iSRD, if that matters). The word from Lasersoft was it must be a hardware issue. I called Epson tech support and they said it was a software issue. Punt, Pass or Kick, I guess?
Anyways, here's what I tried next...which WORKED (!). I deleted the preferences from Silverfast Ai Studio 6.6 and Silverfast HDR Studio 6.6 and guess what? When I went to re-scan using Silverfast 8, the mysterious line was no longer there.
Now if somebody would like to tell me how two versions of an application, one being 32-bit and the other being 64-bit, residing in different directories, could somehow corrupt one another, well, I would love to hear the explanation.
Bizarre, but at least I got it solved.
Thanks again guys for helping me troubleshoot. This forum is orders of magnitude better than Lasersoft's own support forum.