Why would VBA TypeOf operator fail

Question

I have been fighting with an Excel 2007 problem for several days now. Below is a listing of all facts I can think of that might be relevant:

1. IDetailShee

Answer 1

If you're not trusting TypeOf, plough on and ignore errors:

Dim sht as EXCEL.WorkSheet
For Each sht in ActiveWorkbook.Worksheets
  'If TypeOf sht is IDetailSheet Then
  Dim DetailSheet As IDetailSheet
  On Error Resume Next
  Set DetailSheet = sht
  On Error GoTo 0
  If Not DetailSheet Is Nothing Then
    DetailSheets.Add DetailSheet, DetailSheet.Name
  End If
Next sht

If this doesn't work, the worksheets really aren't IDetailSheet at that time at least.