First, in Outlook, I did the following (to add Fax Mail Transport):
Tools/E-mail Accounts/Add a new e-mail account/Additional Server Types/Fax Mail Transport

Next, when I do the following directly in Outlook, it works. The mail is sent to fax server and I also receive a copy via email (like show below).

The problem is when I try to send the same thing programmatically using the following code:

oOutlook = CREATEOBJECT("outlook.application")
oOlItem = oOutlook.CreateItem(0)
oOlItem.To = "me@mycompany.com; [fax: 450 954-1234]"
oOlItem.Subject = "test # 245"  :-)
oOlItem.Attachments.Add("c:\fax-test\myfile.tif", "1")
oOlItem.Send

I receive the mail to my email address, but also a message from System Admin.
In French:
Microsoft Fax Transport n'a pas pu envoyer ce message au destinataire.
Impossible de restituer la totalité des pièces jointes.

In English (translation give me something like):
Microsoft Fax Transport failed to deliver the message to the
recipient. Not all attachments can be rendered.

What's wrong here?

P.S.: I found this link where someone got a similar problem.
http://www.pcreview.co.uk/forums/thread-1827395.php