"attaching html file from app fails", any error message or what?

>Strange problem with email attachments.
>I hv files attached to email in 3 formats
>Txt,Html,Xls.
>If users Outlook default message format is set to HTML
>attaching html file from app fails!
>TXT,XLS gets attached without problems.
>
>I do not want html to be part of email message but sent as attachment.
>
>Any ideas how to resolve it, without renaming html file or forcing
>user to change default format settings ?
>
>TIA