SMTP Transport Sink Event Problem

I am trying to make a sink that will nuke any emails with a small zip file attached.  I have got my users pretty well trained, but sooner or later one is going to do something stupid.

I have written a vbs to do the job (mostly pinched from MS) but I can't seem to get it to fire at all!?  I use the standard MS script to register the event and I says everything is ok but nothing happens.  I have some diagnostic code in there but it does not produce anything.

And yes, I have restarted the Default SMTP server.

The reg code is:
cscript smtpreg.vbs /add 1 onarrival NoSmallZips CDO.SS_SMTPOnArrivalSink "rcpt to=*"
cscript smtpreg.vbs /setprop 1 onarrival NoSmallZips Sink ScriptName "c:\sinkevents\nosmallzips.vbs"

The script is:

<SCRIPT LANGUAGE="VBScript">

Sub IEventIsCacheable_IsCacheable()
      'To implement the interface, and return S_OK implicitly
End Sub

Sub ISMTPOnArrival_OnArrival(ByVal Msg, EventStatus)
      Dim envFlds
      Dim colAttachs
      Dim iFound
      Dim iSize
      
      Set fso = CreateObject("Scripting.FileSystemObject")
      Set wFile = fso.OpenTextFile("c:\nozip_Log.txt", 8, True)
      wfile.WriteLine ("Event Sink Fired at " & Now)

      Set envFlds = Msg.EnvelopeFields
      Set colAttachs = Msg.Attachments

      Wfile.writeline ("Mail from :" & Msg.From)
      Wfile.writeline ("Mail Subject :" & Msg.Subject)


      If Msg.Subject="Zip Test" Then

            For Each oAttach in colAttachs
                  Wfile.writeline ("Filename: " & oAttach.FileName)
                  If InStrRev(oAttach.FileName, ".vbs",-1, 1) = (Len(oAttach.FileName)-3) Then
                        iSize=oAttach.Fields(&H0E200003) 'CdoPR_ATTACH_SIZE
                        Wfile.writeline ("Size :" & iSize)
                        if iSize < 100000  Then
                              iFound = 1
                        End If
                  End If
            Next

            If iFound > 0 Then
                  'Do not deliver, place message in the Badmail directory.
                  envFlds ("http://schemas.microsoft.com/cdo/smtpenvelope/messagestatus") = 3
                  envFlds.Update  'Commit the changes of the message status 'Skip remain event sinks
                  EventStatus = 1
            End If
      End if
End Sub

</SCRIPT>

I do not get anything at all in the log file.

Please tell me I have done something stupid here.