Just paste this source code into a module called basStrings and include it in your project.
'----------------------------------------------------------------------
'
' Module Name: basStrings
' Written By: C&D Programming Corp.
' Create Date: 8/98
' Copyright: Copyright 1998 by C&D Programming Corp. Source
' code may not be reproduced except for use in a
' compiled executable. All rights reserved. If
' you would like to reprint any or all of this
' code please email us at info@codeoftheweek.com
'----------------------------------------------------------------------
Option Explicit
Public Function FindLastOccurrence(sData As String, sSearchString As String) As Long
Dim lPos As Long
Dim lLastPos As Long
On Error Goto Handler
lPos = 0
Do
lLastPos = lPos
lPos = InStr(lPos + 1, sData, sSearchString, vbBinaryCompare)
If lPos = 0 Then Exit Do
Loop
FindLastOccurrence = lLastPos
Exit Function
Handler:
Err.Raise Err.Number, "FindLastOccurrence", Err.Description
End Function