I have taken a credit card across the screen, but without any positive effect. For some reason I could not down load an updated driver from the Canon site I found the other day. I found a different site today which offered a download for driver and a another for a scanner. I have down loaded both my desktop. it is unclear whether they are active, but if so, they have made no difference.
I will try and obtain some Isopropyl alcohol to give the screen a clean, but I'm not sure why that should make any difference, as it still scans photos and scan documents without this issue.
I have downloaded vuescan and the green line still appears on the scanned transparency.
The line is straight and even. Could it really be caused by dust or dirt on the glass. Wouldn't dust or dirt be likely cause an uneven line/effect?
Could a faulty Led cause the problem with transparencies, but not other scans? If so, then it looks like a new scanner.
My only other thought is whether light is creeping in through the edge of the film guide. But it snaps shut and the lid presses down on it when shut, so it seems unlikely and also, as indicated above the the green hue is an even line along all the cells.