@Ztv: you are right, I mean you no disrespect and I apologise for being patronising, if that's the way it came across. It was not intended as such ... more frustration at not being able to get to the bottom of the problem.

@ragulduy: I am inclined to think that it is not the workbook and probably not Excel. If I were a betting man, I would be putting my money on a physical problem, most likely the keyboard. I would want to swap it with another that works on another machine and put the original keyboard on the second machine to see if the fault moves. From the description, I suspect that, for some reason, the key combination is not holding and only the Enter key being pressed is sensed.

@Jonmo1: with regard to your PM, you also are correct ... I pushed too hard, and unnecessarily, to see the "real" workbook. That was for the satisfaction of proving that it was absolutely NOT an issue with the workbook, content, formulas or formatting.

As Sherlock Holmes said: "Eliminate all other factors, and the one which remains must be the truth."

Anyway, I'm going to back right off now and patiently wait for a successful outcome.

Regards, TMS