Ah Graham, you are very perceptive. It was not a time or date formula, but instead I was using a RANK function in one of my worksheets. Every time I opened that workbook, it performed the RANK function thereby constituting a change to the file and prompting the dialogue box in my original question. I isolated by copying one worksheet at a time to a new file until I found which worksheet it was. Then I employed your theory and isolated it down to that stinking RANK function. You were clearly on the right track with your solution and I want to extend a million thank yous for your idea that led to the solution. Now I can sleep peacefully now that my Excel file works the way I want it to (yes, I need to get a life). I wonder if any/all functions have the same affect??
Thanks a million, Graham!
ED