No, è che sono scemo io e mi dimentico i pezzi per strada.
codice:
Public Sub AddDirSep(ByRef Path As String)
    Const PathSep As String = "\"
    If Right$(Path, 1)<>PathSep Then Path = Path + PathSep
End Function

Public Function GetLastModifiedFile(ByVal Directory As String)
    Dim fileName As String
    Dim lastAccessDate As Date
    Dim curLastAccessDate As Date
    AddDirSep(Directory)
    fileName = Dir(Directory + "*.*")
    While fileName<>""
        curLastAccessDate = FileDateTime(Directory + fileName)
        If curLastAccessDate > lastAccessDate Then
            lastAccessDate = curLastAccessDate
            GetLastModifiedFile = Directory + fileName
        End If
        fileName = Dir
    Wend
End Function