Data Validation code error

[sconly]

I'm getting an 'application-defined or object-defined error' error when executing the code below.

it produces the error on the line in red.

[VBA] For r = 4 To 5000
If ActiveSheet.Cells(r, 2).Value = "" Then
ActiveSheet.Range("B" & r).Select
With Selection.Validation
.Delete
.Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _
xlBetween, Formula1:="=buildings"
.IgnoreBlank = True
.InCellDropdown = True
.InputTitle = ""
.ErrorTitle = ""
.InputMessage = ""
.ErrorMessage = ""
.ShowInput = True
.ShowError = True
End With
ActiveSheet.Cells(r, 1).Formula = "=IF(B" & r & "<>"""",VLOOKUP(B" & r & ",Buildings!A:B,2,FALSE)"
Exit For
End If
Next r
[/VBA]

The sheet is not locked/protected and the exact same code works on another workbook that I've created.

Can anyone help?

Thanks.

[Bob Phillips]

I the light of your comments, it would probably help to post the workbook.