1st thing to check would be that it is not a hardware problem. do you have
an optical mouse? Does it need it's batteries changed? Is mouse bottom
clean and clear? Mouse very old and wearing out?

" wrote:

All of the sudden when I am trying to highligt a row of cells by dragging,
the highlighting will drop some of the first cells or jump to other cells and
then I get a message asking if I want to replace the cells with new content.
I'm just trying to copy & paste as I have done for over 10 years!!