The manual says about Delta_YMD:

       This function returns the vector

           ( $year2 - $year1, $month2 - $month1, $day2 - $day1 )

       An error occurs if any of the two dates is invalid.
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Which is exactly what it is doing but, obviously, is not what you want. You would be better off using the Delta_Days() function which will return the difference between the dates in days. This actually makes more sense because expressing the difference in years, months, and days is a bit ambiguous due to the fact that neither a year nor a month has a constant number of days.

-sauoq
"My two cents aren't worth a dime.";