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