Hi Baz,
It's a stuck pixel, because of the way the chip is read out the line carries on from the stuck pixel.
It will darkframe out, but you'll have to take a new set of darks. I had one go on my SBig a couple of months ago, and it was delivered with one.
If the camera is still under warranty then ask the retailer if they'll take it back and replace it.
Attached is a crop of one of my darks 900seconds -15C, the new defect is on the left, just right of centre fullframe.
A bit more info here
www.sbig.com/pdffiles/column_defect.pdf
Cheers
Stuart