Duedate not working with cells with formulas

Is there any way of making duedate works with the cells that has forumlas?

In range D2:D7 there are formulas with dates where message should return saying please check the date which is overdue but the codes does not work

In range D8:D11, these dates are normal without formulas and works with the code

DueDateFail.xls

If I change the code in Sheet1 to D2:D7 the codes won't work but do work with D8:D11 because the dates in D8:D11 don't have the formulas like D2:D7 has

Thanks