Mysterious horizontal black line - solved (Excel 2000)

[ChrisGreaves]

I've had a mysterious horizontal black line stretch across my worksheet for a couple of weeks now.
I finally twigged.
I've been using a background image (Excel 2000: Format, Sheet, Background). The background image is a PrtScr from a PPT 2000 slide with two colors gradation. Makes a nice segue from white to pale blue, to white, to pale blue as one scrolls down.

The PrtScr is pasted into an MSPaint image which I resize to 4x960 pixels after dragging it up to hide the black border.
If I haven't dragged properly, I end up with a 1-pixel row at the foot of the image, and when implemented as a background this arises as a horizontal line across all 256 columns.

I've been poking around with Set Print Area and all sorts of things trying to fathom this one out!

Attached is an example of how NOT to do it - inspect the bottom pixels of the image, you'll see the black line.