This is just a guess, but are the dates stored as text? If you look in the
formula bar, is there an apostrophe in front of the date? The apostrophe
will override any cell formatting you may have.

"Annie" wrote:

When we open a Lotus file in Excel all the data converted properly. Now when
entering a DATEDIF function in a cell it returns a zero (0) answer on any of
the three sheets that were part of the original Lotus file. If we insert a
new sheet DateDif works. If we open an new blank file DateDif works. We
have tired reformatting the cells to numeric and many other formats but
DateDif will not work in the three original sheets of the file. WHy?