I've been using this formula for a couple of years on several sheets.
=IF([Current Month]@row = "1", January@row, IF([Current Month]@row = "2", February@row, IF([Current Month]@row = "3", March@row, IF([Current Month]@row = "4", April@row, IF([Current Month]@row = "5", May@row, IF([Current Month]@row = "6", June@row, [Current Month]@row = "7", July@row, IF([Current Month]@row = "8", August@row, IF([Current Month]@row = "9", September@row, IF([Current Month]@row = "10", October@row, IF([Current Month]@row = "11", November@row, IF([Current Month]@row = "12", December@row)))))))))))
Not pretty I know, but it works. I've just returned from 2 week leave and discovered all of these formulas have fallen over, returning "#INCORRECT ARGUMENT SET" Nobody has touched the formulas or the sheets.
Anybody know what's happened?