=DATEDIF(A18,$A$25,"YD")

Using the above formula if I enter the 15th July 1991 into cell a18 and the 25th June 2007 in cell a25 the formula returns the answer 189.

This is not the correct answer it should I think be 345.

I have used this formula many times and it has always worked and whilst it still does for most dates it now does not work with others. I have recently updated to excel 2007.

Is there a problem with this function in 2007?