Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False
On Error GoTo ErrHandler
Dim rngRef As Excel.Range
Dim rngArea As Excel.Range
Dim rngCells As Excel.Range
Dim rngCell As Excel.Range
Set rngRef = ActiveSheet.UsedRange.Columns
Select Case rngRef
Case Is = "C"
Set rngCells = Intersect(Target, rngRef)
If Not rngCells Is Nothing Then
For Each rngArea In rngCells.Areas
For Each rngCell In rngArea.Cells
With Cells(rngCell.row, "D")
If Trim$(rngCell.Value) <> "" Then
Call .Validation.Delete
Call .ClearContents
Call .Validation.Add(xlValidateList, Formula1:="=Drivers")
Else
Call .Validation.Delete
Call .ClearContents
End If
End With
Next
Next
End If