The form template is a browser-compatible form. If the form is published to a server running InfoPath Forms Services, it ...

The form template is a browser-compatible form. If the form is published to a server running InfoPath Forms Services, it does not have sufficient security permissions to open when sent as an attachment in e-mail messages. To open the form correctly when sent as an e-mail message, ensure that the form template is not sent as an e-mail attachment.