Dropdown lists in excel 2007

Private Sub Worksheet_Change(ByVal Target As Range) 
'Target is the cell or a range of cells whose values were changed
' and that triggered the change. Excel itself will handles this part.
' This code is written with assumption that at a time only
' one cell would be changed

    ' if the changed column is not column A, then we are exiting
    If Target.Column <> 1 Then Exit Sub 

    ' we are disabling excel ability to react when the cell or range is 
    ' changed. It will be enabled later on. This prevents cyclic or
    ' recursive calls     
    Application.EnableEvents = False 
     
    Dim mainsrc As String 
    Dim subsrc As String 
     
    Dim lThisRow As Long 
    ' find which row was modifed that triggered this function to be called
    lThisRow = Target.Row 
    
    ' Check if the value in column A on the row that was changed is ""
    If Cells(lThisRow, 1) = "" Then 

        ' since the value in column A is blank, we are deleting any 
        ' validation from Column B on the same row
        Cells(lThisRow, 2).Validation.Delete 

        ' goto to a label "exit_sub"
        GoTo exit_sub 
    End If 
     

    mainsrc = Cells(lThisRow, 1).Value 
     
    On Error Resume Next 
    'attempting to read what is the current validation formula in cell in
   ' column B of the changed row
    subsrc = Cells(lThisRow, 2).Validation.Formula1 
    On Error GoTo 0 
    
    ' check if the current validation in the column B is same as one that
    ' is needed now due to change in the value of column 1
    If ("=" & subsrc = mainsrc) Then 
        ' the validation I n column B is for same major category
        ' no need to reset validation
        GoTo exit_sub 
    End If 
  
  ' since the major category was changed, we reset any selected value
  ' in column B of the changed row to ""    
  Cells(lThisRow, 2) = "" 

  ' putting the new validation in B
  With Cells(lThisRow, 2).Validation 
        .Delete 
        .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:=xlBetween, Formula1:="=" & mainsrc 
        .IgnoreBlank = True 
        .InCellDropdown = True 
        .InputTitle = "This is my Input Title" 
        .ErrorTitle = "Oops Error" 
        .InputMessage = "Select a Value" 
        .ErrorMessage = "Not a valid value" 
        .ShowInput = True 
        .ShowError = True 
    End With 
     

' a label to allow for "Goto" statement
exit_sub: 
     
    ' re-enabling the ability for excel to react to events/triggers
    Application.EnableEvents = True 

End Sub