Later I found out this is due to the converting from vs2003 to vs2005.

I got the idea for the original solution from the KBase article c2016115 from
http://technicalsupport.businessobjects.com.

Here is a piece of example code:

Private Sub btnFax_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFax.Click
        Dim rtfOpts As New PdfRtfWordFormatOptions
        Dim mailOpts As New MicrosoftMailDestinationOptions
        Dim exportOpts As New ExportOptions

        exportOpts = MyRptDoc.ExportOptions
        With exportOpts
            .ExportDestinationType = ExportDestinationType.MicrosoftMail
            .ExportFormatType = ExportFormatType.WordForWindows
            .DestinationOptions = mailOpts
        End With
        mailOpts.MailMessage = txtDesc.Text
        mailOpts.MailSubject = "Invoice from Company XYZ"
        mailOpts.MailToList = "[Fax:" + Fax + "]"
        With rtfOpts
            .UsePageRange = True
        End With
        MyRptDoc.Export()
        Me.Close()
    End Sub


We use GFI fax drivers. The fax went out with data but no format.

This is quoting from above mentioned KB article, and it is also confirmed from the fax driver vendor:
"The report cannot be sent to the fax driver as a report format, but must be sent in a format that the fax driver recognizes, such as Microsoft Word or RTF".

 

On the other side, all preview, print, email (as attachment in PDF format) are working just fine.