This simple 10 line code doesn't work if just the reference is changed..why?

Hello duugg,

I am guessing you missed changing the Cells references in the code. They are looking at column 2 or "B". If you want to examine cells in column "D" then the column reference needs to be a 4.

Sub Delete_Dup_Customer_Numbers()
r = 1
Do
    Do While Application.WorksheetFunction.CountIf(ActiveSheet.Range("B:B"), Cells(r, 2)) > 1
         ActiveSheet.Range("D:D").Find(Cells(r, 4), Cells(r, 4)).EntireRow.Delete
    Loop
    r = r + 1
Loop Until Cells(r, 2) = ""
End Sub