Excel code stopped working

maybe:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
  on error goto XL90
  If Target.count > 1 Then Exit Sub
  application.screenupdating =False

  With OLEObjects("TempCombo")
    .Visible=false
    If Target.Validation.Type = 3 Then
       .Left = Target.Left
      .Top = Target.Top
      .Width = Target.Width + 15
      .Height = Target.Height + 5
      .ListFillRange = mid(Target.Validation.Formula1,2)
      .LinkedCell = Target.Address
      .Visible=True
    End With
  End If

XL90:
  Application.ScreenUpdating = True
End Sub

If validationrules in the worksheet have been removed the code won't work. Start checking the worksheet.