Problem with attaching files using MAPI in VB??

[Mr_If]

the app send an email message but it won't attach a file to the email. Here is the code I am using to attach the file.
I don't know if I am using this right or not.

Dim objSession As MAPI.Session
Dim objMessage As MAPI.Message

'create a message and fill in its properties
Set objMessage = objSession.Outbox.Messages.Add
objMessage.Subject = txtSubject.Text
objMessage.Text = txtMessage.Text
objMessage.Attachments.Add "C:\file.dat"