Try this:

Sub AAAAA()
   Const FilePath = "D:\Data\"
   Workbooks.Open Filename:=FindNewestFile(FilePath)
End Sub

Function FindNewestFile(FilePath As String) As String
Dim LastDate As Date, NewDate As Date
Dim LastFile As String, NewFile As String
'Check all the .XLS files in the folder.  Find the
'most recent file.
LastFile$ = LCase$(Dir(FilePath$ & "*.XLS"))
LastDate = FileDateTime(FilePath$ & LastFile$)
NewFile$ = LastFile$
Do While Len(NewFile$) > 0
   NewFile$ = LCase$(Dir())
   If Len(NewFile$) = 0 Then Exit Do
   NewDate = FileDateTime(FilePath$ & NewFile$)
   If NewDate > LastDate Then
       LastDate = NewDate
       LastFile$ = NewFile$
   End If
Loop
FindNewestFile$ = FilePath$ & LastFile$
End Function

Hope this helps,

Hutch